2 files changed, 14 insertions, 4 deletions
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 3e6bd5a2efb..b0d6901953f 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -143,12 +143,14 @@ Sema::CheckFunctionCall(FunctionDecl *FDecl, CallExpr *TheCall) {
   // Printf checking.
   if (const FormatAttr *Format = FDecl->getAttr<FormatAttr>()) {
     if (Format->getType() == "printf") {
-      bool HasVAListArg = false;
-      if (const FunctionProtoType *Proto 
-          = FDecl->getType()->getAsFunctionProtoType())
+      bool HasVAListArg = Format->getFirstArg() == 0;
+      if (!HasVAListArg) {
+        if (const FunctionProtoType *Proto 
+            = FDecl->getType()->getAsFunctionProtoType())
         HasVAListArg = !Proto->isVariadic();
+      }
       CheckPrintfArguments(TheCall, HasVAListArg, Format->getFormatIdx() - 1,
-                           Format->getFirstArg() - 1);
+                           HasVAListArg ? 0 : Format->getFirstArg() - 1);
     }
   }
 
diff --git a/clang/test/Sema/format-attribute.c b/clang/test/Sema/format-attribute.c
index ecdef9dde1a..a1cd0b84b37 100644
--- a/clang/test/Sema/format-attribute.c
+++ b/clang/test/Sema/format-attribute.c
@@ -24,3 +24,11 @@ struct _mystruct {
 };
 
 typedef int (*f3_ptr)(char*,...) __attribute__((format(printf,1,0))); // no-error
+
+// <rdar://problem/6623513>
+int rdar6623513(void *, const char*, const char*, ...)
+  __attribute__ ((format (printf, 3, 0)));
+
+int rdar6623513_aux(int len, const char* s) {
+  rdar6623513(0, "hello", "%.*s", len, s);
+}