diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 2b38718..2ee9e84 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -7974,6 +7974,13 @@
                                              "printf", 2,
                                              Name->isStr("vasprintf") ? 0 : 3));
   }
+
+  if (Name->isStr("__CFStringMakeConstantString")) {
+    // We already have a __builtin___CFStringMakeConstantString,
+    // but builds that use -fno-constant-cfstrings don't go through that.
+    if (!FD->getAttr<FormatArgAttr>())
+      FD->addAttr(::new (Context) FormatArgAttr(FD->getLocation(), Context, 1));
+  }
 }
 
 TypedefDecl *Sema::ParseTypedefDecl(Scope *S, Declarator &D, QualType T,
diff --git a/test/SemaObjC/format-strings-objc.m b/test/SemaObjC/format-strings-objc.m
index 840694a..7faa995 100644
--- a/test/SemaObjC/format-strings-objc.m
+++ b/test/SemaObjC/format-strings-objc.m
@@ -34,9 +34,9 @@
 #define CFSTR(cStr)  ((CFStringRef) __builtin___CFStringMakeConstantString ("" cStr ""))
 
 // This function is used instead of the builtin if -fno-constant-cfstrings.
-// The definition on Mac OS X is NOT annotated with format_arg as of 10.7,
-// but if it were, we want the same checking behavior as with the builtin.
-extern CFStringRef __CFStringMakeConstantString(const char *) __attribute__((format_arg(1)));
+// The definition on Mac OS X is NOT annotated with format_arg as of 10.8,
+// but clang will implicitly add the attribute if it's not written.
+extern CFStringRef __CFStringMakeConstantString(const char *);
 
 int printf(const char * restrict, ...) ;