diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index 09ebbc085fe5..2a54bcc3afbd 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -2560,6 +2560,17 @@ static bool handleFunctionTypeAttr(TypeProcessingState &state,
     if (!unwrapped.isFunctionType())
       return false;
 
+    // Diagnose regparm with fastcall.
+    const FunctionType *fn = unwrapped.get();
+    CallingConv CC = fn->getCallConv();
+    if (CC == CC_X86FastCall) {
+      S.Diag(attr.getLoc(), diag::err_attributes_are_not_compatible)
+        << FunctionType::getNameForCallConv(CC)
+        << "regparm";
+      attr.setInvalid();
+      return true;
+    }
+
     FunctionType::ExtInfo EI = 
       unwrapped.get()->getExtInfo().withRegParm(value);
     type = unwrapped.wrap(S, S.Context.adjustFunctionType(unwrapped.get(), EI));
@@ -2578,7 +2589,8 @@ static bool handleFunctionTypeAttr(TypeProcessingState &state,
   CallingConv CCOld = fn->getCallConv();
   if (S.Context.getCanonicalCallConv(CC) ==
       S.Context.getCanonicalCallConv(CCOld)) {
-    attr.setInvalid();
+    FunctionType::ExtInfo EI= unwrapped.get()->getExtInfo().withCallingConv(CC);
+    type = unwrapped.wrap(S, S.Context.adjustFunctionType(unwrapped.get(), EI));
     return true;
   }
 
@@ -2607,6 +2619,15 @@ static bool handleFunctionTypeAttr(TypeProcessingState &state,
       attr.setInvalid();
       return true;
     }
+
+    // Also diagnose fastcall with regparm.
+    if (fn->getRegParmType()) {
+      S.Diag(attr.getLoc(), diag::err_attributes_are_not_compatible)
+        << "regparm"
+        << FunctionType::getNameForCallConv(CC);
+      attr.setInvalid();
+      return true;
+    }
   }
 
   FunctionType::ExtInfo EI = unwrapped.get()->getExtInfo().withCallingConv(CC);
diff --git a/clang/test/Sema/stdcall-fastcall.c b/clang/test/Sema/stdcall-fastcall.c
index dffcb969a997..4531eb2a81c8 100644
--- a/clang/test/Sema/stdcall-fastcall.c
+++ b/clang/test/Sema/stdcall-fastcall.c
@@ -8,3 +8,13 @@ int __attribute__((fastcall)) var2; // expected-warning{{'fastcall' only applies
 void __attribute__((stdcall, fastcall)) foo3(void); // expected-error{{fastcall and stdcall attributes are not compatible}}
 void __attribute__((stdcall)) foo4(); // expected-note{{previous declaration is here}}
 void __attribute__((fastcall)) foo4(void); // expected-error{{function declared 'fastcall' here was previously declared 'stdcall'}}
+
+// rdar://8876096
+void rdar8876096foo1(int i, int j) __attribute__((fastcall, cdecl)); // expected-error {{not compatible}}
+void rdar8876096foo2(int i, int j) __attribute__((fastcall, stdcall)); // expected-error {{not compatible}}
+void rdar8876096foo3(int i, int j) __attribute__((fastcall, regparm(2))); // expected-error {{not compatible}}
+void rdar8876096foo4(int i, int j) __attribute__((stdcall, cdecl)); // expected-error {{not compatible}}
+void rdar8876096foo5(int i, int j) __attribute__((stdcall, fastcall)); // expected-error {{not compatible}}
+void rdar8876096foo6(int i, int j) __attribute__((cdecl, fastcall)); // expected-error {{not compatible}}
+void rdar8876096foo7(int i, int j) __attribute__((cdecl, stdcall)); // expected-error {{not compatible}}
+void rdar8876096foo8(int i, int j) __attribute__((regparm(2), fastcall)); // expected-error {{not compatible}}