diff --git a/src/Compiler/Checking/CheckExpressions.fs b/src/Compiler/Checking/CheckExpressions.fs
index 02a69da16ce..f2a0877cace 100644
--- a/src/Compiler/Checking/CheckExpressions.fs
+++ b/src/Compiler/Checking/CheckExpressions.fs
@@ -431,9 +431,9 @@ type cenv = TcFileState
 let CopyAndFixupTypars g m rigid tpsorig =
     FreshenAndFixupTypars g m rigid [] [] tpsorig
 
-let UnifyTypes (cenv: cenv) (env: TcEnv) m actualTy expectedTy =
+let UnifyTypes (cenv: cenv) (env: TcEnv) m expectedTy actualTy =
     let g = cenv.g
-    AddCxTypeEqualsType env.eContextInfo env.DisplayEnv cenv.css m (tryNormalizeMeasureInType g actualTy) (tryNormalizeMeasureInType g expectedTy)
+    AddCxTypeEqualsType env.eContextInfo env.DisplayEnv cenv.css m (tryNormalizeMeasureInType g expectedTy) (tryNormalizeMeasureInType g actualTy)
 
 // If the overall type admits subsumption or type directed conversion, and the original unify would have failed,
 // then allow subsumption or type directed conversion.
@@ -5884,10 +5884,10 @@ and CheckTupleIsCorrectLength g (env: TcEnv) m tupleTy (args: 'a list) tcArgs =
         if args.Length <> ptys.Length then
             let argTys = NewInferenceTypes g args
             suppressErrorReporting (fun () -> tcArgs argTys)
-            let expectedTy = TType_tuple (tupInfo, argTys)
+            let actualTy = TType_tuple (tupInfo, argTys)
 
             // We let error recovery handle this exception
-            error (ErrorFromAddingTypeEquation(g, env.DisplayEnv, tupleTy, expectedTy,
+            error (ErrorFromAddingTypeEquation(g, env.DisplayEnv, tupleTy, actualTy,
                    (ConstraintSolverTupleDiffLengths(env.DisplayEnv, env.eContextInfo, ptys, argTys, m, m)), m))
 
 and TcExprTuple (cenv: cenv) overallTy env tpenv (isExplicitStruct, args, m) =
diff --git a/src/Compiler/Checking/CheckExpressions.fsi b/src/Compiler/Checking/CheckExpressions.fsi
index b26381b6b02..0ecc045f05d 100644
--- a/src/Compiler/Checking/CheckExpressions.fsi
+++ b/src/Compiler/Checking/CheckExpressions.fsi
@@ -863,7 +863,7 @@ val TranslateSynValInfo:
 val TranslatePartialValReprInfo: tps: Typar list -> PrelimValReprInfo -> ValReprInfo
 
 /// Constrain two types to be equal within this type checking context
-val UnifyTypes: cenv: TcFileState -> env: TcEnv -> m: range -> actualTy: TType -> expectedTy: TType -> unit
+val UnifyTypes: cenv: TcFileState -> env: TcEnv -> m: range -> expectedTy: TType -> actualTy: TType -> unit
 
 val TcRuntimeTypeTest:
     isCast: bool ->
diff --git a/src/Compiler/Checking/ConstraintSolver.fs b/src/Compiler/Checking/ConstraintSolver.fs
index fa20b108362..e999152ce54 100644
--- a/src/Compiler/Checking/ConstraintSolver.fs
+++ b/src/Compiler/Checking/ConstraintSolver.fs
@@ -246,9 +246,9 @@ exception ConstraintSolverError of string * range * range
 
 exception ErrorFromApplyingDefault of tcGlobals: TcGlobals * displayEnv: DisplayEnv * Typar * TType * error: exn * range: range
 
-exception ErrorFromAddingTypeEquation of tcGlobals: TcGlobals * displayEnv: DisplayEnv * actualTy: TType * expectedTy: TType * error: exn * range: range
+exception ErrorFromAddingTypeEquation of tcGlobals: TcGlobals * displayEnv: DisplayEnv * expectedTy: TType * actualTy: TType * error: exn * range: range
 
-exception ErrorsFromAddingSubsumptionConstraint of tcGlobals: TcGlobals * displayEnv: DisplayEnv * actualTy: TType * expectedTy: TType * error: exn * ctxtInfo: ContextInfo * parameterRange: range
+exception ErrorsFromAddingSubsumptionConstraint of tcGlobals: TcGlobals * displayEnv: DisplayEnv * expectedTy: TType * actualTy: TType * error: exn * ctxtInfo: ContextInfo * parameterRange: range
 
 exception ErrorFromAddingConstraint of displayEnv: DisplayEnv * error: exn * range: range
 
@@ -2732,12 +2732,12 @@ and SolveTypeSubsumesTypeWithWrappedContextualReport (csenv: ConstraintSolverEnv
 and SolveTypeSubsumesTypeWithReport (csenv: ConstraintSolverEnv) ndeep m trace cxsln origTy1 ty1 ty2 =
     SolveTypeSubsumesTypeWithWrappedContextualReport csenv ndeep m trace cxsln origTy1 ty1 ty2 id
 
-and SolveTypeEqualsTypeWithReport (csenv: ConstraintSolverEnv) ndeep m trace cxsln actualTy expectedTy = 
+and SolveTypeEqualsTypeWithReport (csenv: ConstraintSolverEnv) ndeep m trace cxsln expectedTy actualTy =
     TryD
-        (fun () -> SolveTypeEqualsTypeKeepAbbrevsWithCxsln csenv ndeep m trace cxsln actualTy expectedTy)
+        (fun () -> SolveTypeEqualsTypeKeepAbbrevsWithCxsln csenv ndeep m trace cxsln expectedTy actualTy)
         (function
         | AbortForFailedMemberConstraintResolution as err -> ErrorD err
-        | res -> ErrorD (ErrorFromAddingTypeEquation(csenv.g, csenv.DisplayEnv, actualTy, expectedTy, res, m)))
+        | res -> ErrorD (ErrorFromAddingTypeEquation(csenv.g, csenv.DisplayEnv, expectedTy, actualTy, res, m)))
   
 and ArgsMustSubsumeOrConvert 
         (csenv: ConstraintSolverEnv)
@@ -3478,10 +3478,10 @@ let EliminateConstraintsForGeneralizedTypars (denv: DisplayEnv) css m (trace: Op
 // No error recovery here: we do that on a per-expression basis.
 //------------------------------------------------------------------------- 
 
-let AddCxTypeEqualsType contextInfo denv css m actual expected  = 
+let AddCxTypeEqualsType contextInfo denv css m expected actual =
     let csenv = MakeConstraintSolverEnv contextInfo css m denv
     PostponeOnFailedMemberConstraintResolution csenv NoTrace
-        (fun csenv -> SolveTypeEqualsTypeWithReport csenv 0 m NoTrace None actual expected)
+        (fun csenv -> SolveTypeEqualsTypeWithReport csenv 0 m NoTrace None expected actual)
         ErrorD
     |> RaiseOperationResult
 
diff --git a/src/Compiler/Checking/ConstraintSolver.fsi b/src/Compiler/Checking/ConstraintSolver.fsi
index d6cc309c6b5..eb48ce3b439 100644
--- a/src/Compiler/Checking/ConstraintSolver.fsi
+++ b/src/Compiler/Checking/ConstraintSolver.fsi
@@ -187,16 +187,16 @@ exception ErrorFromApplyingDefault of
 exception ErrorFromAddingTypeEquation of
     tcGlobals: TcGlobals *
     displayEnv: DisplayEnv *
-    actualTy: TType *
     expectedTy: TType *
+    actualTy: TType *
     error: exn *
     range: range
 
 exception ErrorsFromAddingSubsumptionConstraint of
     tcGlobals: TcGlobals *
     displayEnv: DisplayEnv *
-    actualTy: TType *
     expectedTy: TType *
+    actualTy: TType *
     error: exn *
     ctxtInfo: ContextInfo *
     parameterRange: range