diff --git a/docs/release-notes/.FSharp.Compiler.Service/8.0.400.md b/docs/release-notes/.FSharp.Compiler.Service/8.0.400.md
index 17ccb2f4019..e4f784a1045 100644
--- a/docs/release-notes/.FSharp.Compiler.Service/8.0.400.md
+++ b/docs/release-notes/.FSharp.Compiler.Service/8.0.400.md
@@ -14,3 +14,7 @@
 ### Added
 
 * Generate new `Equals` overload to avoid boxing for structural comparison ([PR #16857](https://github.com/dotnet/fsharp/pull/16857))
+
+### Changed
+
+* Improve error of Active Pattern case Argument Count Not Match ([PR #16846](https://github.com/dotnet/fsharp/pull/16846))
diff --git a/src/Compiler/Checking/CheckExpressions.fs b/src/Compiler/Checking/CheckExpressions.fs
index 16e46ae706b..5d42f2fd416 100644
--- a/src/Compiler/Checking/CheckExpressions.fs
+++ b/src/Compiler/Checking/CheckExpressions.fs
@@ -5119,22 +5119,77 @@ and TcPatLongIdentActivePatternCase warnOnUpper (cenv: cenv) (env: TcEnv) vFlags
     let vExprTy = vExpr.Type
 
     let activePatArgsAsSynPats, patArg =
-        match args with
-        | [] -> [], SynPat.Const(SynConst.Unit, m)
-        | _ ->
-            // This bit of type-directed analysis ensures that parameterized partial active patterns returning unit do not need to take an argument
-            let dtys, retTy = stripFunTy g vExprTy
-
-            if dtys.Length = args.Length + 1 &&
-                ((isOptionTy g retTy && isUnitTy g (destOptionTy g retTy)) ||
-                (isValueOptionTy g retTy && isUnitTy g (destValueOptionTy g retTy))) ||
-                // `bool` partial AP always be treated as `unit option`
-                // For `val (|P|_|) : _ -> bool`, only allow `match x with | P -> ...`
-                // For `val (|P|_|) : _ -> _ -> bool`, only allow `match x with | P parameter -> ...`
-                (not apinfo.IsTotal && isBoolTy g retTy) then
+        let rec IsNotSolved ty =
+            match ty with
+            | TType_var(v, _) when v.IsSolved ->
+                match v.Solution with
+                | Some t -> IsNotSolved t
+                | None -> false
+            | TType_var _ -> true
+            | _ -> false
+
+        // only cases which return unit or unresolved type (in AP definition) can omit output arg 
+        let canOmit retTy = isUnitTy g retTy || IsNotSolved retTy 
+
+        // This bit of type-directed analysis ensures that parameterized partial active patterns returning unit do not need to take an argument
+        let dtys, retTy = stripFunTy g vExprTy
+        let paramCount = if dtys.Length = 0 then 0 else dtys.Length - 1
+
+        let showErrMsg returnCount =
+            let fmtExprArgs paramCount =
+                let rec loop i (sb: Text.StringBuilder) =
+                    let cutoff = 10
+                    if i > paramCount then sb.ToString()
+                    elif i > cutoff then sb.Append("...").ToString()
+                    else loop (i + 1) (sb.Append(" e").Append i)
+            
+                loop 1 (Text.StringBuilder())
+
+            let caseName = apinfo.ActiveTags[idx]
+            let msg =
+                match paramCount, returnCount with
+                | 0, 0 -> FSComp.SR.tcActivePatternArgsCountNotMatchNoArgsNoPat(caseName, caseName)
+                | 0, _ -> FSComp.SR.tcActivePatternArgsCountNotMatchOnlyPat(caseName)
+                | _, 0 -> FSComp.SR.tcActivePatternArgsCountNotMatchArgs(paramCount, caseName, fmtExprArgs paramCount)
+                | _, _ -> FSComp.SR.tcActivePatternArgsCountNotMatchArgsAndPat(paramCount, caseName, fmtExprArgs paramCount)
+            error(Error(msg, m))
+
+        // partial active pattern (returning bool) doesn't have output arg
+        if (not apinfo.IsTotal && isBoolTy g retTy) then
+            checkLanguageFeatureError g.langVersion LanguageFeature.BooleanReturningAndReturnTypeDirectedPartialActivePattern m
+            if paramCount = List.length args then
                 args, SynPat.Const(SynConst.Unit, m)
             else
-                List.frontAndBack args
+                showErrMsg 0
+
+        // for single case active pattern, if not all parameter provided, output will be a function
+        // that takes the remaining parameter as input
+        elif apinfo.IsTotal && apinfo.ActiveTags.Length = 1 && dtys.Length >= args.Length && not args.IsEmpty then
+            List.frontAndBack args
+
+        // active pattern cases returning unit or unknown things (in AP definition) can omit output arg 
+        elif paramCount = args.Length then
+             let caseRetTy =
+                 if isOptionTy g retTy then destOptionTy g retTy
+                 elif isValueOptionTy g retTy then destValueOptionTy g retTy
+                 elif isChoiceTy g retTy then destChoiceTy g retTy idx
+                 else retTy
+
+             // only cases which return unit or unresolved type (in AP definition) can omit output arg 
+             if canOmit caseRetTy then
+                args, SynPat.Const(SynConst.Unit, m)
+             else
+                 showErrMsg 1
+        
+        // active pattern in function param (e.g. let f (|P|_|) = ...)
+        elif IsNotSolved vExprTy then
+            List.frontAndBack args
+
+        // args count should equal to AP function params count
+        elif dtys.Length <> args.Length then
+            showErrMsg 1
+        else
+            List.frontAndBack args
 
     if not (isNil activePatArgsAsSynPats) && apinfo.ActiveTags.Length <> 1 then
         errorR (Error (FSComp.SR.tcRequireActivePatternWithOneResult (), m))
diff --git a/src/Compiler/FSComp.txt b/src/Compiler/FSComp.txt
index d7dfe371f3e..25047f08e39 100644
--- a/src/Compiler/FSComp.txt
+++ b/src/Compiler/FSComp.txt
@@ -1747,4 +1747,8 @@ featureReuseSameFieldsInStructUnions,"Share underlying fields in a [<Struct>] di
 3864,tooManyMethodsInDotNetTypeWritingAssembly,"The type '%s' has too many methods. Found: '%d', maximum: '%d'"
 3865,parsOnlySimplePatternsAreAllowedInConstructors,"Only simple patterns are allowed in primary constructors"
 3866,chkStaticAbstractInterfaceMembers,"A static abstract non-virtual interface member should only be called via type parameter (for example: 'T.%s)."
-3867,chkStaticAbstractMembersOnClasses,"Classes cannot contain static abstract members."
\ No newline at end of file
+3867,chkStaticAbstractMembersOnClasses,"Classes cannot contain static abstract members."
+3868,tcActivePatternArgsCountNotMatchNoArgsNoPat,"This active pattern does not expect any arguments, i.e., it should be used like '%s' instead of '%s x'."
+3868,tcActivePatternArgsCountNotMatchOnlyPat,"This active pattern expects exactly one pattern argument, e.g., '%s pat'."
+3868,tcActivePatternArgsCountNotMatchArgs,"This active pattern expects %d expression argument(s), e.g., '%s%s'."
+3868,tcActivePatternArgsCountNotMatchArgsAndPat,"This active pattern expects %d expression argument(s) and a pattern argument, e.g., '%s%s pat'."
diff --git a/src/Compiler/TypedTree/TypedTreeOps.fs b/src/Compiler/TypedTree/TypedTreeOps.fs
index eb2ceb9a6aa..02a5497cbb1 100644
--- a/src/Compiler/TypedTree/TypedTreeOps.fs
+++ b/src/Compiler/TypedTree/TypedTreeOps.fs
@@ -3689,6 +3689,17 @@ let isOptionTy (g: TcGlobals) ty =
     | ValueNone -> false
     | ValueSome tcref -> tyconRefEq g g.option_tcr_canon tcref
 
+let isChoiceTy (g: TcGlobals) ty = 
+    match tryTcrefOfAppTy g ty with 
+    | ValueNone -> false
+    | ValueSome tcref ->
+        tyconRefEq g g.choice2_tcr tcref ||
+        tyconRefEq g g.choice3_tcr tcref ||
+        tyconRefEq g g.choice4_tcr tcref ||
+        tyconRefEq g g.choice5_tcr tcref ||
+        tyconRefEq g g.choice6_tcr tcref ||
+        tyconRefEq g g.choice7_tcr tcref
+
 let tryDestOptionTy g ty = 
     match argsOfAppTy g ty with 
     | [ty1] when isOptionTy g ty -> ValueSome ty1
@@ -3699,6 +3710,11 @@ let tryDestValueOptionTy g ty =
     | [ty1] when isValueOptionTy g ty -> ValueSome ty1
     | _ -> ValueNone
 
+let tryDestChoiceTy g ty idx = 
+    match argsOfAppTy g ty with 
+    | ls when isChoiceTy g ty && ls.Length > idx -> ValueSome ls[idx]
+    | _ -> ValueNone
+
 let destOptionTy g ty = 
     match tryDestOptionTy g ty with 
     | ValueSome ty -> ty
@@ -3709,6 +3725,11 @@ let destValueOptionTy g ty =
     | ValueSome ty -> ty
     | ValueNone -> failwith "destValueOptionTy: not a value option type"
 
+let destChoiceTy g ty idx = 
+    match tryDestChoiceTy g ty idx with 
+    | ValueSome ty -> ty
+    | ValueNone -> failwith "destChoiceTy: not a Choice type"
+
 let isNullableTy (g: TcGlobals) ty = 
     match tryTcrefOfAppTy g ty with 
     | ValueNone -> false
diff --git a/src/Compiler/TypedTree/TypedTreeOps.fsi b/src/Compiler/TypedTree/TypedTreeOps.fsi
index 258cf320bc8..1740cbb530d 100755
--- a/src/Compiler/TypedTree/TypedTreeOps.fsi
+++ b/src/Compiler/TypedTree/TypedTreeOps.fsi
@@ -1547,6 +1547,9 @@ val isValueOptionTy: TcGlobals -> TType -> bool
 /// Determine if a type is an option type
 val isOptionTy: TcGlobals -> TType -> bool
 
+/// Determine if a type is an Choice type
+val isChoiceTy: TcGlobals -> TType -> bool
+
 /// Take apart an option type
 val destOptionTy: TcGlobals -> TType -> TType
 
@@ -1556,6 +1559,12 @@ val tryDestOptionTy: TcGlobals -> TType -> TType voption
 /// Try to take apart an option type
 val destValueOptionTy: TcGlobals -> TType -> TType
 
+/// Take apart an Choice type
+val tryDestChoiceTy: TcGlobals -> TType -> int -> TType voption
+
+/// Try to take apart an Choice type
+val destChoiceTy: TcGlobals -> TType -> int -> TType
+
 /// Determine is a type is a System.Nullable type
 val isNullableTy: TcGlobals -> TType -> bool
 
diff --git a/src/Compiler/xlf/FSComp.txt.cs.xlf b/src/Compiler/xlf/FSComp.txt.cs.xlf
index 1e331ca0c1e..a4e8e281866 100644
--- a/src/Compiler/xlf/FSComp.txt.cs.xlf
+++ b/src/Compiler/xlf/FSComp.txt.cs.xlf
@@ -1122,6 +1122,26 @@
         <target state="translated">(Navržený název)</target>
         <note />
       </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgs">
+        <source>This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgsAndPat">
+        <source>This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchNoArgsNoPat">
+        <source>This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</source>
+        <target state="new">This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchOnlyPat">
+        <source>This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</source>
+        <target state="new">This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="tcAmbiguousDiscardDotLambda">
         <source>The meaning of _ is ambiguous here. It cannot be used for a discarded variable and a function shorthand in the same scope.</source>
         <target state="translated">Význam _ je tady nejednoznačný. Nelze ho použít pro proměnnou typu discard a zkratku funkce ve stejném oboru.</target>
diff --git a/src/Compiler/xlf/FSComp.txt.de.xlf b/src/Compiler/xlf/FSComp.txt.de.xlf
index cb5bb611c16..f920991d5f4 100644
--- a/src/Compiler/xlf/FSComp.txt.de.xlf
+++ b/src/Compiler/xlf/FSComp.txt.de.xlf
@@ -1122,6 +1122,26 @@
         <target state="translated">(Empfohlener Name)</target>
         <note />
       </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgs">
+        <source>This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgsAndPat">
+        <source>This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchNoArgsNoPat">
+        <source>This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</source>
+        <target state="new">This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchOnlyPat">
+        <source>This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</source>
+        <target state="new">This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="tcAmbiguousDiscardDotLambda">
         <source>The meaning of _ is ambiguous here. It cannot be used for a discarded variable and a function shorthand in the same scope.</source>
         <target state="translated">Die Bedeutung von "_" ist hier mehrdeutig. Dieses Zeichen kann nicht in demselben Bereich für eine verworfene Variable und ein Funktionskürzel verwendet werden.</target>
diff --git a/src/Compiler/xlf/FSComp.txt.es.xlf b/src/Compiler/xlf/FSComp.txt.es.xlf
index 5a5520af8d0..f6054605ffa 100644
--- a/src/Compiler/xlf/FSComp.txt.es.xlf
+++ b/src/Compiler/xlf/FSComp.txt.es.xlf
@@ -1122,6 +1122,26 @@
         <target state="translated">(Nombre sugerido)</target>
         <note />
       </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgs">
+        <source>This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgsAndPat">
+        <source>This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchNoArgsNoPat">
+        <source>This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</source>
+        <target state="new">This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchOnlyPat">
+        <source>This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</source>
+        <target state="new">This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="tcAmbiguousDiscardDotLambda">
         <source>The meaning of _ is ambiguous here. It cannot be used for a discarded variable and a function shorthand in the same scope.</source>
         <target state="translated">El significado de _ es ambiguo aquí. No se puede usar para una variable descartada y una función abreviada en el mismo ámbito.</target>
diff --git a/src/Compiler/xlf/FSComp.txt.fr.xlf b/src/Compiler/xlf/FSComp.txt.fr.xlf
index 95f24fd7db2..5e9349ac3ae 100644
--- a/src/Compiler/xlf/FSComp.txt.fr.xlf
+++ b/src/Compiler/xlf/FSComp.txt.fr.xlf
@@ -1122,6 +1122,26 @@
         <target state="translated">(Nom suggéré)</target>
         <note />
       </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgs">
+        <source>This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgsAndPat">
+        <source>This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchNoArgsNoPat">
+        <source>This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</source>
+        <target state="new">This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchOnlyPat">
+        <source>This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</source>
+        <target state="new">This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="tcAmbiguousDiscardDotLambda">
         <source>The meaning of _ is ambiguous here. It cannot be used for a discarded variable and a function shorthand in the same scope.</source>
         <target state="translated">La signification de _ est ici ambiguë. Il ne peut pas être utilisé pour une variable ignorée et un raccourci de fonction dans la même portée.</target>
diff --git a/src/Compiler/xlf/FSComp.txt.it.xlf b/src/Compiler/xlf/FSComp.txt.it.xlf
index a4468df7f8e..b936cdc3642 100644
--- a/src/Compiler/xlf/FSComp.txt.it.xlf
+++ b/src/Compiler/xlf/FSComp.txt.it.xlf
@@ -1122,6 +1122,26 @@
         <target state="translated">(Nome consigliato)</target>
         <note />
       </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgs">
+        <source>This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgsAndPat">
+        <source>This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchNoArgsNoPat">
+        <source>This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</source>
+        <target state="new">This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchOnlyPat">
+        <source>This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</source>
+        <target state="new">This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="tcAmbiguousDiscardDotLambda">
         <source>The meaning of _ is ambiguous here. It cannot be used for a discarded variable and a function shorthand in the same scope.</source>
         <target state="translated">Il significato di _ è ambiguo in questo contesto. Non può essere utilizzato per una variabile eliminata e una sintassi abbreviata di funzione nello stesso ambito.</target>
diff --git a/src/Compiler/xlf/FSComp.txt.ja.xlf b/src/Compiler/xlf/FSComp.txt.ja.xlf
index 358cf700cf0..add97ebcbee 100644
--- a/src/Compiler/xlf/FSComp.txt.ja.xlf
+++ b/src/Compiler/xlf/FSComp.txt.ja.xlf
@@ -1122,6 +1122,26 @@
         <target state="translated">(推奨される名前)</target>
         <note />
       </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgs">
+        <source>This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgsAndPat">
+        <source>This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchNoArgsNoPat">
+        <source>This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</source>
+        <target state="new">This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchOnlyPat">
+        <source>This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</source>
+        <target state="new">This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="tcAmbiguousDiscardDotLambda">
         <source>The meaning of _ is ambiguous here. It cannot be used for a discarded variable and a function shorthand in the same scope.</source>
         <target state="translated">ここでは _ の意味はあいまいです。破棄された変数と、同じスコープ内の関数の短縮形には使用できません。</target>
diff --git a/src/Compiler/xlf/FSComp.txt.ko.xlf b/src/Compiler/xlf/FSComp.txt.ko.xlf
index 5784d4264e1..005109642a3 100644
--- a/src/Compiler/xlf/FSComp.txt.ko.xlf
+++ b/src/Compiler/xlf/FSComp.txt.ko.xlf
@@ -1122,6 +1122,26 @@
         <target state="translated">(제안된 이름)</target>
         <note />
       </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgs">
+        <source>This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgsAndPat">
+        <source>This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchNoArgsNoPat">
+        <source>This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</source>
+        <target state="new">This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchOnlyPat">
+        <source>This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</source>
+        <target state="new">This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="tcAmbiguousDiscardDotLambda">
         <source>The meaning of _ is ambiguous here. It cannot be used for a discarded variable and a function shorthand in the same scope.</source>
         <target state="translated">여기서 _의 의미가 모호합니다. 삭제된 변수와 동일한 범위의 함수 줄임에는 사용할 수 없습니다.</target>
diff --git a/src/Compiler/xlf/FSComp.txt.pl.xlf b/src/Compiler/xlf/FSComp.txt.pl.xlf
index f2858d49504..b11a525807f 100644
--- a/src/Compiler/xlf/FSComp.txt.pl.xlf
+++ b/src/Compiler/xlf/FSComp.txt.pl.xlf
@@ -1122,6 +1122,26 @@
         <target state="translated">(Sugerowana nazwa)</target>
         <note />
       </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgs">
+        <source>This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgsAndPat">
+        <source>This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchNoArgsNoPat">
+        <source>This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</source>
+        <target state="new">This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchOnlyPat">
+        <source>This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</source>
+        <target state="new">This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="tcAmbiguousDiscardDotLambda">
         <source>The meaning of _ is ambiguous here. It cannot be used for a discarded variable and a function shorthand in the same scope.</source>
         <target state="translated">Znaczenie elementu _ jest tutaj niejednoznaczne. Nie można go użyć dla odrzuconej zmiennej i skrótu funkcji w tym samym zakresie.</target>
diff --git a/src/Compiler/xlf/FSComp.txt.pt-BR.xlf b/src/Compiler/xlf/FSComp.txt.pt-BR.xlf
index cdff3ed5b34..78b23fc160d 100644
--- a/src/Compiler/xlf/FSComp.txt.pt-BR.xlf
+++ b/src/Compiler/xlf/FSComp.txt.pt-BR.xlf
@@ -1122,6 +1122,26 @@
         <target state="translated">(Nome sugerido)</target>
         <note />
       </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgs">
+        <source>This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgsAndPat">
+        <source>This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchNoArgsNoPat">
+        <source>This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</source>
+        <target state="new">This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchOnlyPat">
+        <source>This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</source>
+        <target state="new">This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="tcAmbiguousDiscardDotLambda">
         <source>The meaning of _ is ambiguous here. It cannot be used for a discarded variable and a function shorthand in the same scope.</source>
         <target state="translated">O significado de _ é ambíguo aqui. Ele não pode ser usado para uma variável descartada e uma abreviação de função no mesmo escopo.</target>
diff --git a/src/Compiler/xlf/FSComp.txt.ru.xlf b/src/Compiler/xlf/FSComp.txt.ru.xlf
index 9d1790e8dc9..670b03ce32a 100644
--- a/src/Compiler/xlf/FSComp.txt.ru.xlf
+++ b/src/Compiler/xlf/FSComp.txt.ru.xlf
@@ -1122,6 +1122,26 @@
         <target state="translated">(предложенное имя)</target>
         <note />
       </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgs">
+        <source>This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgsAndPat">
+        <source>This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchNoArgsNoPat">
+        <source>This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</source>
+        <target state="new">This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchOnlyPat">
+        <source>This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</source>
+        <target state="new">This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="tcAmbiguousDiscardDotLambda">
         <source>The meaning of _ is ambiguous here. It cannot be used for a discarded variable and a function shorthand in the same scope.</source>
         <target state="translated">Неоднозначное значение символа _ здесь. Его нельзя использовать для пустой переменной и сокращенной функции в одной области.</target>
diff --git a/src/Compiler/xlf/FSComp.txt.tr.xlf b/src/Compiler/xlf/FSComp.txt.tr.xlf
index b8bdd5e9cc6..e0552438c26 100644
--- a/src/Compiler/xlf/FSComp.txt.tr.xlf
+++ b/src/Compiler/xlf/FSComp.txt.tr.xlf
@@ -1122,6 +1122,26 @@
         <target state="translated">(Önerilen ad)</target>
         <note />
       </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgs">
+        <source>This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgsAndPat">
+        <source>This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchNoArgsNoPat">
+        <source>This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</source>
+        <target state="new">This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchOnlyPat">
+        <source>This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</source>
+        <target state="new">This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="tcAmbiguousDiscardDotLambda">
         <source>The meaning of _ is ambiguous here. It cannot be used for a discarded variable and a function shorthand in the same scope.</source>
         <target state="translated">_ öğesinin anlamı burada belirsiz. Aynı kapsamda, atılan bir değişken ve işlev kısaltması için kullanılamaz.</target>
diff --git a/src/Compiler/xlf/FSComp.txt.zh-Hans.xlf b/src/Compiler/xlf/FSComp.txt.zh-Hans.xlf
index f06487e86bd..f53a45b0200 100644
--- a/src/Compiler/xlf/FSComp.txt.zh-Hans.xlf
+++ b/src/Compiler/xlf/FSComp.txt.zh-Hans.xlf
@@ -1122,6 +1122,26 @@
         <target state="translated">(建议名称)</target>
         <note />
       </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgs">
+        <source>This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgsAndPat">
+        <source>This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchNoArgsNoPat">
+        <source>This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</source>
+        <target state="new">This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchOnlyPat">
+        <source>This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</source>
+        <target state="new">This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="tcAmbiguousDiscardDotLambda">
         <source>The meaning of _ is ambiguous here. It cannot be used for a discarded variable and a function shorthand in the same scope.</source>
         <target state="translated">此处的 _ 含义不明确。它不能用于同一范围内的已放弃变量和函数速记。</target>
diff --git a/src/Compiler/xlf/FSComp.txt.zh-Hant.xlf b/src/Compiler/xlf/FSComp.txt.zh-Hant.xlf
index f80470220b3..a80e8852c30 100644
--- a/src/Compiler/xlf/FSComp.txt.zh-Hant.xlf
+++ b/src/Compiler/xlf/FSComp.txt.zh-Hant.xlf
@@ -1122,6 +1122,26 @@
         <target state="translated">(建議的名稱)</target>
         <note />
       </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgs">
+        <source>This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s), e.g., '{1}{2}'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchArgsAndPat">
+        <source>This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</source>
+        <target state="new">This active pattern expects {0} expression argument(s) and a pattern argument, e.g., '{1}{2} pat'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchNoArgsNoPat">
+        <source>This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</source>
+        <target state="new">This active pattern does not expect any arguments, i.e., it should be used like '{0}' instead of '{1} x'.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="tcActivePatternArgsCountNotMatchOnlyPat">
+        <source>This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</source>
+        <target state="new">This active pattern expects exactly one pattern argument, e.g., '{0} pat'.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="tcAmbiguousDiscardDotLambda">
         <source>The meaning of _ is ambiguous here. It cannot be used for a discarded variable and a function shorthand in the same scope.</source>
         <target state="translated">此處的 _ 意義不明確。它不能在同一個範圍中既作為已捨棄的變數又作為函式速記。</target>
diff --git a/tests/FSharp.Compiler.ComponentTests/ErrorMessages/ActivePatternArgCountMismatchTest.fs b/tests/FSharp.Compiler.ComponentTests/ErrorMessages/ActivePatternArgCountMismatchTest.fs
new file mode 100644
index 00000000000..77fd98449b0
--- /dev/null
+++ b/tests/FSharp.Compiler.ComponentTests/ErrorMessages/ActivePatternArgCountMismatchTest.fs
@@ -0,0 +1,40 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace ErrorMessages
+
+open Xunit
+open FSharp.Test.Compiler
+
+module ``Active Pattern argument count mismatch test`` =
+
+    [<Fact>]
+    let ``test``() =
+        FSharp """
+let (|IsEven|_|) x = x % 2 = 0
+match 1 with
+| IsEven xxx -> ()
+| _ -> printfn "Odd!"
+
+let (|Ignore|) x = ()
+match 1 with
+| Ignore () () -> printfn "Ignored!"
+| _ -> ()
+
+let (|Equals|_|) z y x = x = y
+match 1 with
+| Equals "" 2 xxx -> ()
+| _ -> printfn "Not Equal"
+
+let (|A|) a b c d = d
+match 1 with
+| A -> ()
+| _ -> ()
+        """ |> withLangVersionPreview
+            |> typecheck
+            |> shouldFail
+            |> withDiagnostics [
+        (Error 3868, Line 4, Col 3, Line 4, Col 13, "This active pattern does not expect any arguments, i.e., it should be used like 'IsEven' instead of 'IsEven x'.")
+        (Error 3868, Line 9, Col 3, Line 9, Col 15, "This active pattern expects exactly one pattern argument, e.g., 'Ignore pat'.")
+        (Error 3868, Line 14, Col 3, Line 14, Col 18, "This active pattern expects 2 expression argument(s), e.g., 'Equals e1 e2'.")
+        (Error 3868, Line 19, Col 3, Line 19, Col 4, "This active pattern expects 3 expression argument(s) and a pattern argument, e.g., 'A e1 e2 e3 pat'.")
+    ]
diff --git a/tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj b/tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj
index 6924b94f448..fec09aa52d9 100644
--- a/tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj
+++ b/tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj
@@ -208,6 +208,7 @@
     <Compile Include="ErrorMessages\UnionCasePatternMatchingErrors.fs" />
     <Compile Include="ErrorMessages\InterfaceImplInAugmentationsTests.fs" />
     <Compile Include="ErrorMessages\ExtendedDiagnosticDataTests.fs" />
+    <Compile Include="ErrorMessages\ActivePatternArgCountMismatchTest.fs" />
     <Compile Include="Language\IndexerSetterParamArray.fs" />
     <Compile Include="Language\MultiDimensionalArrayTests.fs" />
     <Compile Include="Language\RegressionTests.fs" />
@@ -331,6 +332,7 @@
     <Content Include="resources\**" CopyToOutputDirectory="Never" CopyToPublishDirectory="PreserveNewest" />
     <EmbeddedResource Remove="Properties\**" />
     <None Remove="EmittedIL\GenericComparison\CrossAssembly.fs" />
+    <None Remove="ErrorMessages\ActivePatternArgCountMismatchTest.fs" />
     <Content Include="xunit.runner.json" CopyToOutputDirectory="PreserveNewest" />
   </ItemGroup>
 
diff --git a/tests/FSharp.Compiler.ComponentTests/Language/BooleanReturningAndReturnTypeDirectedPartialActivePatternTests.fs b/tests/FSharp.Compiler.ComponentTests/Language/BooleanReturningAndReturnTypeDirectedPartialActivePatternTests.fs
index 26461598a5b..c8ba6fba856 100644
--- a/tests/FSharp.Compiler.ComponentTests/Language/BooleanReturningAndReturnTypeDirectedPartialActivePatternTests.fs
+++ b/tests/FSharp.Compiler.ComponentTests/Language/BooleanReturningAndReturnTypeDirectedPartialActivePatternTests.fs
@@ -75,7 +75,8 @@ let (|OddVOption|_|) x = if x % 2 = 1 then ValueSome() else ValueNone
 
 [<Fact>]
 let ``Can not receive result from bool active pattern`` () =
-    FSharp """let (|IsA|_|) x = x = "A"
+    FSharp """#nowarn "20"
+let (|IsA|_|) x = x = "A"
 
 match "A" with 
 | IsA result -> "A" 
@@ -93,34 +94,9 @@ match "A" with
     |> typecheck
     |> shouldFail
     |> withDiagnostics [
-        (Error 1, Line 4, Col 3, Line 4, Col 13,
-         "This expression was expected to have type
-    'string -> bool'    
-but here has type
-    'bool'    ")
-        (Error 39, Line 4, Col 7, Line 4, Col 13,
-         "The value or constructor 'result' is not defined. Maybe you want one of the following:
+        (Error 3868, Line 5, Col 3, Line 5, Col 13, "This active pattern does not expect any arguments, i.e., it should be used like 'IsA' instead of 'IsA x'.")
+        (Error 3868, Line 9, Col 3, Line 9, Col 13, "This active pattern does not expect any arguments, i.e., it should be used like 'IsA' instead of 'IsA x'.")
+        (Error 0039, Line 9, Col 17, Line 9, Col 23, "The value or constructor 'result' is not defined. Maybe you want one of the following:
    Result")
-        (Warning 20, Line 3, Col 1, Line 5, Col 15,
-         "The result of this expression has type 'string' and is implicitly ignored. Consider using 'ignore' to discard this value explicitly, e.g. 'expr |> ignore', or 'let' to bind the result to a name, e.g. 'let result = expr'.");
-        (Error 1, Line 8, Col 3, Line 8, Col 13,
-         "This expression was expected to have type
-    'string -> bool'    
-but here has type
-    'bool'    ")
-        (Error 39, Line 8, Col 7, Line 8, Col 13,
-         "The value or constructor 'result' is not defined. Maybe you want one of the following:
-   Result");
-        (Error 39, Line 8, Col 17, Line 8, Col 23,
-         "The value or constructor 'result' is not defined. Maybe you want one of the following:
-   Result")
-        (Warning 20, Line 7, Col 1, Line 9, Col 15,
-         "The result of this expression has type 'string' and is implicitly ignored. Consider using 'ignore' to discard this value explicitly, e.g. 'expr |> ignore', or 'let' to bind the result to a name, e.g. 'let result = expr'.");
-        (Error 1, Line 12, Col 3, Line 12, Col 30,
-         "This expression was expected to have type
-    'string -> bool'    
-but here has type
-    'bool'    ")
-        (Warning 20, Line 11, Col 1, Line 13, Col 21,
-         "The result of this expression has type 'string' and is implicitly ignored. Consider using 'ignore' to discard this value explicitly, e.g. 'expr |> ignore', or 'let' to bind the result to a name, e.g. 'let result = expr'.")
+        (Error 3868, Line 13, Col 3, Line 13, Col 30, "This active pattern does not expect any arguments, i.e., it should be used like 'IsA' instead of 'IsA x'.")
     ]