diff --git a/clang/include/clang/Basic/TargetInfo.h b/clang/include/clang/Basic/TargetInfo.h
index d136b459e9cd4..d5089faa41174 100644
--- a/clang/include/clang/Basic/TargetInfo.h
+++ b/clang/include/clang/Basic/TargetInfo.h
@@ -253,7 +253,7 @@ class TargetInfo : public TransferrableTargetInfo,
   const char *MCountName;
   unsigned char RegParmMax, SSERegParmMax;
   TargetCXXABI TheCXXABI;
-  bool UseMicrosoftManglingForC = false;
+  bool UseMicrosoftCCForC = false;
   const LangASMap *AddrSpaceMap;
 
   mutable StringRef PlatformName;
@@ -1345,10 +1345,8 @@ class TargetInfo : public TransferrableTargetInfo,
     return TheCXXABI;
   }
 
-  /// Should the Microsoft mangling scheme be used for C Calling Convention.
-  bool shouldUseMicrosoftCCforMangling() const {
-    return UseMicrosoftManglingForC;
-  }
+  /// Should the Microsoft C Calling Convention be used.
+  bool shouldUseMicrosoftCCforC() const { return UseMicrosoftCCForC; }
 
   /// Target the specified CPU.
   ///
diff --git a/clang/lib/AST/Mangle.cpp b/clang/lib/AST/Mangle.cpp
index b44ab23f1d0e1..515a2217e7e6b 100644
--- a/clang/lib/AST/Mangle.cpp
+++ b/clang/lib/AST/Mangle.cpp
@@ -74,7 +74,7 @@ static CCMangling getCallingConvMangling(const ASTContext &Context,
       if (FD->isMain() && FD->getNumParams() == 2)
         return CCM_WasmMainArgcArgv;
 
-  if (!TI.shouldUseMicrosoftCCforMangling())
+  if (!TI.shouldUseMicrosoftCCforC())
     return CCM_Other;
 
   if (Context.getLangOpts().CPlusPlus && !isExternC(ND) &&
diff --git a/clang/lib/Basic/Targets/OSTargets.h b/clang/lib/Basic/Targets/OSTargets.h
index a88c851797aab..777b768b282f0 100644
--- a/clang/lib/Basic/Targets/OSTargets.h
+++ b/clang/lib/Basic/Targets/OSTargets.h
@@ -817,7 +817,7 @@ class LLVM_LIBRARY_VISIBILITY UEFITargetInfo : public OSTargetInfo<Target> {
       : OSTargetInfo<Target>(Triple, Opts) {
     this->WCharType = TargetInfo::UnsignedShort;
     this->WIntType = TargetInfo::UnsignedShort;
-    this->UseMicrosoftManglingForC = true;
+    this->UseMicrosoftCCForC = true;
   }
 };
 
@@ -838,7 +838,7 @@ class LLVM_LIBRARY_VISIBILITY WindowsTargetInfo : public OSTargetInfo<Target> {
       : OSTargetInfo<Target>(Triple, Opts) {
     this->WCharType = TargetInfo::UnsignedShort;
     this->WIntType = TargetInfo::UnsignedShort;
-    this->UseMicrosoftManglingForC = true;
+    this->UseMicrosoftCCForC = true;
   }
 };
 
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index a6cdbbafec666..42a61a3570405 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -4769,11 +4769,12 @@ ExprResult Sema::CheckOSLogFormatStringArg(Expr *Arg) {
 /// Check that the user is calling the appropriate va_start builtin for the
 /// target and calling convention.
 static bool checkVAStartABI(Sema &S, unsigned BuiltinID, Expr *Fn) {
-  const llvm::Triple &TT = S.Context.getTargetInfo().getTriple();
+  const TargetInfo &TI = S.Context.getTargetInfo();
+  bool IsMicrosoftCC = TI.shouldUseMicrosoftCCforC();
+  const llvm::Triple &TT = TI.getTriple();
   bool IsX64 = TT.getArch() == llvm::Triple::x86_64;
   bool IsAArch64 = (TT.getArch() == llvm::Triple::aarch64 ||
                     TT.getArch() == llvm::Triple::aarch64_32);
-  bool IsWindows = TT.isOSWindows();
   bool IsMSVAStart = BuiltinID == Builtin::BI__builtin_ms_va_start;
   if (IsX64 || IsAArch64) {
     CallingConv CC = CC_C;
@@ -4781,7 +4782,7 @@ static bool checkVAStartABI(Sema &S, unsigned BuiltinID, Expr *Fn) {
       CC = FD->getType()->castAs<FunctionType>()->getCallConv();
     if (IsMSVAStart) {
       // Don't allow this in System V ABI functions.
-      if (CC == CC_X86_64SysV || (!IsWindows && CC != CC_Win64))
+      if (CC == CC_X86_64SysV || (!IsMicrosoftCC && CC != CC_Win64))
         return S.Diag(Fn->getBeginLoc(),
                       diag::err_ms_va_start_used_in_sysv_function);
     } else {
@@ -4789,11 +4790,11 @@ static bool checkVAStartABI(Sema &S, unsigned BuiltinID, Expr *Fn) {
       // On x64 Windows, don't allow this in System V ABI functions.
       // (Yes, that means there's no corresponding way to support variadic
       // System V ABI functions on Windows.)
-      if ((IsWindows && CC == CC_X86_64SysV) ||
-          (!IsWindows && CC == CC_Win64))
+      if ((IsMicrosoftCC && CC == CC_X86_64SysV) ||
+          (!IsMicrosoftCC && CC == CC_Win64))
         return S.Diag(Fn->getBeginLoc(),
                       diag::err_va_start_used_in_wrong_abi_function)
-               << !IsWindows;
+               << !IsMicrosoftCC;
     }
     return false;
   }
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index a36a2f563739e..014c11fd7e74c 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -17990,7 +17990,7 @@ static bool isPotentiallyConstantEvaluatedContext(Sema &SemaRef) {
 static bool funcHasParameterSizeMangling(Sema &S, FunctionDecl *FD) {
   // These manglings are only applicable for targets whcih use Microsoft
   // mangling scheme for C.
-  if (!S.Context.getTargetInfo().shouldUseMicrosoftCCforMangling())
+  if (!S.Context.getTargetInfo().shouldUseMicrosoftCCforC())
     return false;
 
   // If this is C++ and this isn't an extern "C" function, parameters do not
diff --git a/clang/test/Sema/varargs.c b/clang/test/Sema/varargs.c
index bec41dda65d57..2bca4d9e74172 100644
--- a/clang/test/Sema/varargs.c
+++ b/clang/test/Sema/varargs.c
@@ -1,5 +1,8 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s -triple i386-pc-unknown
+// RUN: %clang_cc1 -fsyntax-only -verify %s -triple i386-mingw32
 // RUN: %clang_cc1 -fsyntax-only -verify %s -triple x86_64-apple-darwin9
+// RUN: %clang_cc1 -fsyntax-only -verify %s -triple x86_64-mingw64
+// RUN: %clang_cc1 -fsyntax-only -verify %s -triple x86_64-uefi
 // RUN: %clang_cc1 -fsyntax-only -fms-compatibility -DMS -verify %s -triple x86_64-pc-win32
 
 void f1(int a)