diff --git a/lib/CodeGen/Mangle.cpp b/lib/CodeGen/Mangle.cpp
index f007539..f310e98 100644
--- a/lib/CodeGen/Mangle.cpp
+++ b/lib/CodeGen/Mangle.cpp
@@ -62,14 +62,14 @@
   // FIXME: Actually use a visitor to decode these?
   if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
     bool RequiresMangling = false;
-    // No mangled in an "implicit extern C" header.
-    if (Context.getSourceManager().getFileCharacteristic(FD->getLocation())
-          == SrcMgr::C_ExternCSystem)
-      RequiresMangling = false;
     // Clang's "overloadable" attribute extension to C/C++ implies
     // name mangling (always).
-    else if (FD->getAttr<OverloadableAttr>())
+    if (FD->getAttr<OverloadableAttr>())
       RequiresMangling = true;
+    // No mangled in an "implicit extern C" header.
+    else if (Context.getSourceManager().getFileCharacteristic(FD->getLocation())
+          == SrcMgr::C_ExternCSystem)
+      RequiresMangling = false;
     else if (Context.getLangOptions().CPlusPlus) {
       // C++ requires name mangling, unless we're in a C linkage
       // specification.
diff --git a/test/CodeGen/mangle.c b/test/CodeGen/mangle.c
new file mode 100644
index 0000000..fbee412
--- /dev/null
+++ b/test/CodeGen/mangle.c
@@ -0,0 +1,9 @@
+// RUN: clang -arch i386 -emit-llvm -o %t %s &&
+// RUN: grep '@_Z2f0i' %t &&
+// RUN: grep '@_Z2f0l' %t
+
+// Make sure we mangle overloadable, even in C system headers.
+
+# 1 "somesystemheader.h" 1 3 4
+void __attribute__((__overloadable__)) f0(int a) {}
+void __attribute__((__overloadable__)) f0(long b) {}