diff --git a/clang/include/clang/Sema/SemaInternal.h b/clang/include/clang/Sema/SemaInternal.h
index 563cc1998330..4ee10478e487 100644
--- a/clang/include/clang/Sema/SemaInternal.h
+++ b/clang/include/clang/Sema/SemaInternal.h
@@ -25,6 +25,18 @@ inline PartialDiagnostic Sema::PDiag(unsigned DiagID) {
   return PartialDiagnostic(DiagID, Context.getDiagAllocator());
 }
 
+inline bool
+FTIHasSingleVoidParameter(const DeclaratorChunk::FunctionTypeInfo &FTI) {
+  return FTI.NumParams == 1 && !FTI.isVariadic && FTI.Params[0].Ident == 0 &&
+         FTI.Params[0].Param &&
+         cast<ParmVarDecl>(FTI.Params[0].Param)->getType()->isVoidType();
+}
+
+inline bool
+FTIHasNonVoidParameters(const DeclaratorChunk::FunctionTypeInfo &FTI) {
+  // Assume FTI is well-formed.
+  return FTI.NumParams && !FTIHasSingleVoidParameter(FTI);
+}
 
 // This requires the variable to be non-dependent and the initializer
 // to not be value dependent.
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 0ffce40e1ea2..b7c681f08e2e 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -2658,7 +2658,7 @@ bool Sema::MergeFunctionDecl(FunctionDecl *New, NamedDecl *&OldD,
       New->setType(NewQType);
       New->setHasInheritedPrototype();
 
-      // Synthesize a parameter for each argument type.
+      // Synthesize parameters with the same types.
       SmallVector<ParmVarDecl*, 16> Params;
       for (const auto &ParamType : OldProto->param_types()) {
         ParmVarDecl *Param = ParmVarDecl::Create(Context, New, SourceLocation(),
@@ -6992,11 +6992,7 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
     // single void argument.
     // We let through "const void" here because Sema::GetTypeForDeclarator
     // already checks for that case.
-    if (FTI.NumParams == 1 && !FTI.isVariadic && FTI.Params[0].Ident == 0 &&
-        FTI.Params[0].Param &&
-        cast<ParmVarDecl>(FTI.Params[0].Param)->getType()->isVoidType()) {
-      // Empty arg list, don't push any params.
-    } else if (FTI.NumParams > 0 && FTI.Params[0].Param != 0) {
+    if (FTIHasNonVoidParameters(FTI) && FTI.Params[0].Param) {
       for (unsigned i = 0, e = FTI.NumParams; i != e; ++i) {
         ParmVarDecl *Param = cast<ParmVarDecl>(FTI.Params[i].Param);
         assert(Param->getDeclContext() != NewFD && "Was set before ?");
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 217588a9c099..ef4f8dd4e6a7 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -6252,13 +6252,6 @@ bool Sema::CheckDestructor(CXXDestructorDecl *Destructor) {
   return false;
 }
 
-static inline bool
-FTIHasSingleVoidArgument(DeclaratorChunk::FunctionTypeInfo &FTI) {
-  return (FTI.NumParams == 1 && !FTI.isVariadic && FTI.Params[0].Ident == 0 &&
-          FTI.Params[0].Param &&
-          cast<ParmVarDecl>(FTI.Params[0].Param)->getType()->isVoidType());
-}
-
 /// CheckDestructorDeclarator - Called by ActOnDeclarator to check
 /// the well-formednes of the destructor declarator @p D with type @p
 /// R. If there are any errors in the declarator, this routine will
@@ -6337,7 +6330,7 @@ QualType Sema::CheckDestructorDeclarator(Declarator &D, QualType R,
   }
   
   // Make sure we don't have any parameters.
-  if (FTI.NumParams > 0 && !FTIHasSingleVoidArgument(FTI)) {
+  if (FTIHasNonVoidParameters(FTI)) {
     Diag(D.getIdentifierLoc(), diag::err_destructor_with_params);
 
     // Delete the parameters.
diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
index 7c4f60e51171..e6c714eb9111 100644
--- a/clang/lib/Sema/SemaLambda.cpp
+++ b/clang/lib/Sema/SemaLambda.cpp
@@ -898,10 +898,7 @@ void Sema::ActOnStartOfLambdaDefinition(LambdaIntroducer &Intro,
 
     ExplicitResultType = FTI.hasTrailingReturnType();
 
-    if (FTI.NumParams == 1 && !FTI.isVariadic && FTI.Params[0].Ident == 0 &&
-        cast<ParmVarDecl>(FTI.Params[0].Param)->getType()->isVoidType()) {
-      // Empty arg list, don't push any params.
-    } else {
+    if (FTIHasNonVoidParameters(FTI)) {
       Params.reserve(FTI.NumParams);
       for (unsigned i = 0, e = FTI.NumParams; i != e; ++i)
         Params.push_back(cast<ParmVarDecl>(FTI.Params[i].Param));
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index 0afbe01586d7..448c89071604 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -2330,7 +2330,7 @@ static void checkQualifiedFunction(Sema &S, QualType T,
     << getFunctionQualifiersAsString(T->castAs<FunctionProtoType>());
 }
 
-/// Produce an approprioate diagnostic for an ambiguity between a function
+/// Produce an appropriate diagnostic for an ambiguity between a function
 /// declarator and a C++ direct-initializer.
 static void warnAboutAmbiguousFunction(Sema &S, Declarator &D,
                                        DeclaratorChunk &DeclType, QualType RT) {