diff --git a/src/Compiler/Checking/FindUnsolved.fs b/src/Compiler/Checking/FindUnsolved.fs
index 3a3b8c9de89..26b34d50b19 100644
--- a/src/Compiler/Checking/FindUnsolved.fs
+++ b/src/Compiler/Checking/FindUnsolved.fs
@@ -8,6 +8,7 @@ open Internal.Utilities.Library
 open Internal.Utilities.Library.Extras
 open FSharp.Compiler
 open FSharp.Compiler.DiagnosticsLogger
+open FSharp.Compiler.Text
 open FSharp.Compiler.TypedTree
 open FSharp.Compiler.TypedTreeBasics
 open FSharp.Compiler.TypedTreeOps
@@ -29,14 +30,17 @@ type cenv =
     override _.ToString() = "<cenv>"
 
 /// Walk types, collecting type variables
-let accTy cenv _env ty =
+let accTy cenv _env (fallbackRange: Range option) ty =
     let normalizedTy = tryNormalizeMeasureInType cenv.g ty
     (freeInType CollectTyparsNoCaching normalizedTy).FreeTypars |> Zset.iter (fun tp -> 
-        if (tp.Rigidity <> TyparRigidity.Rigid) then 
+        if (tp.Rigidity <> TyparRigidity.Rigid) then
+            match fallbackRange with
+            | Some r when tp.Range = Range.range0 -> tp.SetIdent (FSharp.Compiler.Syntax.Ident(tp.typar_id.idText, r))
+            | _ -> ()
             cenv.unsolved <- tp :: cenv.unsolved) 
 
 let accTypeInst cenv env tyargs =
-    tyargs |> List.iter (accTy cenv env)
+    tyargs |> List.iter (accTy cenv env None)
 
 /// Walk expressions, collecting type variables
 let rec accExpr (cenv: cenv) (env: env) expr =
@@ -52,17 +56,17 @@ let rec accExpr (cenv: cenv) (env: env) expr =
         accBind cenv env bind  
         accExpr cenv env body
 
-    | Expr.Const (_, _, ty) -> 
-        accTy cenv env ty 
+    | Expr.Const (_, r, ty) -> 
+        accTy cenv env (Some r) ty 
     
     | Expr.Val (_v, _vFlags, _m) -> ()
 
-    | Expr.Quote (ast, _, _, _m, ty) -> 
+    | Expr.Quote (ast, _, _, m, ty) -> 
         accExpr cenv env ast
-        accTy cenv env ty
+        accTy cenv env (Some m) ty
 
-    | Expr.Obj (_, ty, basev, basecall, overrides, iimpls, _m) -> 
-        accTy cenv env ty
+    | Expr.Obj (_, ty, basev, basecall, overrides, iimpls, m) -> 
+        accTy cenv env (Some m) ty
         accExpr cenv env basecall
         accMethods cenv env basev overrides 
         accIntfImpls cenv env basev iimpls
@@ -77,8 +81,8 @@ let rec accExpr (cenv: cenv) (env: env) expr =
     | Expr.Op (c, tyargs, args, m) ->
         accOp cenv env (c, tyargs, args, m) 
 
-    | Expr.App (f, fty, tyargs, argsl, _m) ->
-        accTy cenv env fty
+    | Expr.App (f, fty, tyargs, argsl, m) ->
+        accTy cenv env (Some m) fty
         accTypeInst cenv env tyargs
         accExpr cenv env f
         accExprs cenv env argsl
@@ -88,9 +92,9 @@ let rec accExpr (cenv: cenv) (env: env) expr =
         let ty = mkMultiLambdaTy cenv.g m argvs bodyTy 
         accLambdas cenv env valReprInfo expr ty
 
-    | Expr.TyLambda (_, tps, _body, _m, bodyTy)  -> 
+    | Expr.TyLambda (_, tps, _body, m, bodyTy)  -> 
         let valReprInfo = ValReprInfo (ValReprInfo.InferTyparInfo tps, [], ValReprInfo.unnamedRetVal) 
-        accTy cenv env bodyTy
+        accTy cenv env (Some m) bodyTy
         let ty = mkForallTyIfNeeded tps bodyTy 
         accLambdas cenv env valReprInfo expr ty
 
@@ -98,7 +102,7 @@ let rec accExpr (cenv: cenv) (env: env) expr =
         accExpr cenv env e1 
 
     | Expr.Match (_, _exprm, dtree, targets, m, ty) -> 
-        accTy cenv env ty
+        accTy cenv env (Some m) ty
         accDTree cenv env dtree
         accTargets cenv env m ty targets
 
@@ -106,15 +110,15 @@ let rec accExpr (cenv: cenv) (env: env) expr =
         accBinds cenv env binds
         accExpr cenv env e
 
-    | Expr.StaticOptimization (constraints, e2, e3, _m) -> 
+    | Expr.StaticOptimization (constraints, e2, e3, m) -> 
         accExpr cenv env e2
         accExpr cenv env e3
         constraints |> List.iter (function 
             | TTyconEqualsTycon(ty1, ty2) -> 
-                accTy cenv env ty1
-                accTy cenv env ty2
+                accTy cenv env (Some m) ty1
+                accTy cenv env (Some m) ty2
             | TTyconIsStruct(ty1) -> 
-                accTy cenv env ty1)
+                accTy cenv env (Some m) ty1)
 
     | Expr.WitnessArg (traitInfo, _m) ->
         accTraitInfo cenv env traitInfo
@@ -136,7 +140,7 @@ and accIntfImpls cenv env baseValOpt l =
     List.iter (accIntfImpl cenv env baseValOpt) l
 
 and accIntfImpl cenv env baseValOpt (ty, overrides) = 
-    accTy cenv env ty
+    accTy cenv env None ty
     accMethods cenv env baseValOpt overrides 
 
 and accOp cenv env (op, tyargs, args, _m) =
@@ -158,16 +162,16 @@ and accOp cenv env (op, tyargs, args, _m) =
 
 and accTraitInfo cenv env (TTrait(tys, _nm, _, argTys, retTy, _sln)) =
     argTys |> accTypeInst cenv env 
-    retTy |> Option.iter (accTy cenv env)
-    tys |> List.iter (accTy cenv env)
+    retTy |> Option.iter (accTy cenv env None)
+    tys |> List.iter (accTy cenv env None)
 
 and accLambdas cenv env valReprInfo expr exprTy =
     match stripDebugPoints expr with
     | Expr.TyChoose (_tps, bodyExpr, _m)  -> accLambdas cenv env valReprInfo bodyExpr exprTy      
-    | Expr.Lambda _
-    | Expr.TyLambda _ ->
+    | Expr.Lambda (range = range)
+    | Expr.TyLambda (range = range) ->
         let _tps, ctorThisValOpt, baseValOpt, vsl, body, bodyTy = destLambdaWithValReprInfo cenv.g cenv.amap valReprInfo (expr, exprTy) 
-        accTy cenv env bodyTy
+        accTy cenv env (Some range) bodyTy
         vsl |> List.iterSquared (accVal cenv env)
         baseValOpt |> Option.iter (accVal cenv env)
         ctorThisValOpt |> Option.iter (accVal cenv env)
@@ -198,23 +202,23 @@ and accSwitch cenv env (e, cases, dflt, _m) =
 and accDiscrim cenv env d =
     match d with 
     | DecisionTreeTest.UnionCase(_ucref, tinst) -> accTypeInst cenv env tinst 
-    | DecisionTreeTest.ArrayLength(_, ty) -> accTy cenv env ty
+    | DecisionTreeTest.ArrayLength(_, ty) -> accTy cenv env None ty
     | DecisionTreeTest.Const _
     | DecisionTreeTest.IsNull -> ()
-    | DecisionTreeTest.IsInst (srcTy, tgtTy) -> accTy cenv env srcTy; accTy cenv env tgtTy
+    | DecisionTreeTest.IsInst (srcTy, tgtTy) -> accTy cenv env None srcTy; accTy cenv env None tgtTy
     | DecisionTreeTest.ActivePatternCase (exp, tys, _, _, _, _) -> 
         accExpr cenv env exp
         accTypeInst cenv env tys
     | DecisionTreeTest.Error _ -> ()
 
-and accAttrib cenv env (Attrib(_, _k, args, props, _, _, _m)) = 
+and accAttrib cenv env (Attrib(_, _k, args, props, _, _, m)) = 
     args |> List.iter (fun (AttribExpr(expr1, expr2)) -> 
         accExpr cenv env expr1
         accExpr cenv env expr2)
     props |> List.iter (fun (AttribNamedArg(_nm, ty, _flg, AttribExpr(expr, expr2))) -> 
         accExpr cenv env expr
         accExpr cenv env expr2
-        accTy cenv env ty)
+        accTy cenv env (Some m) ty)
   
 and accAttribs cenv env attribs = 
     List.iter (accAttrib cenv env) attribs
@@ -229,7 +233,7 @@ and accArgReprInfo cenv env (argInfo: ArgReprInfo) =
 and accVal cenv env v =
     v.Attribs |> accAttribs cenv env
     v.ValReprInfo |> Option.iter (accValReprInfo cenv env)
-    v.Type |> accTy cenv env 
+    v.Type |> accTy cenv env None 
 
 and accBind cenv env (bind: Binding) =
     accVal cenv env bind.Var