diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 87d096d..8247d1a 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -9281,6 +9281,11 @@
     if (!IsVariadic)
       return CC_X86VectorCall;
     break;
+  case LangOptions::DCC_RegCall:
+    // __regcall cannot be applied to variadic functions.
+    if (!IsVariadic)
+      return CC_X86RegCall;
+    break;
   }
   return Target->getDefaultCallingConv(TargetInfo::CCMT_Unknown);
 }