diff --git a/lib/CodeGen/Mangle.cpp b/lib/CodeGen/Mangle.cpp
index b7d8e27..c246bb5 100644
--- a/lib/CodeGen/Mangle.cpp
+++ b/lib/CodeGen/Mangle.cpp
@@ -362,12 +362,6 @@
   mangleBareFunctionType(FT, MangleReturnType);
 }
 
-/// isStd - Return whether a given namespace is the 'std' namespace.
-static bool isStd(const NamespaceDecl *NS) {
-  const IdentifierInfo *II = NS->getOriginalNamespace()->getIdentifier();
-  return II && II->isStr("std");
-}
-
 static const DeclContext *IgnoreLinkageSpecDecls(const DeclContext *DC) {
   while (isa<LinkageSpecDecl>(DC)) {
     DC = DC->getParent();
@@ -376,15 +370,21 @@
   return DC;
 }
 
+/// isStd - Return whether a given namespace is the 'std' namespace.
+static bool isStd(const NamespaceDecl *NS) {
+  if (!IgnoreLinkageSpecDecls(NS->getParent())->isTranslationUnit())
+    return false;
+  
+  const IdentifierInfo *II = NS->getOriginalNamespace()->getIdentifier();
+  return II && II->isStr("std");
+}
+
 // isStdNamespace - Return whether a given decl context is a toplevel 'std'
 // namespace.
 static bool isStdNamespace(const DeclContext *DC) {
   if (!DC->isNamespace())
     return false;
 
-  if (!IgnoreLinkageSpecDecls(DC->getParent())->isTranslationUnit())
-    return false;
-
   return isStd(cast<NamespaceDecl>(DC));
 }
 
diff --git a/test/CodeGenCXX/mangle-subst-std.cpp b/test/CodeGenCXX/mangle-subst-std.cpp
index 4c15eaa..9c1e978 100644
--- a/test/CodeGenCXX/mangle-subst-std.cpp
+++ b/test/CodeGenCXX/mangle-subst-std.cpp
@@ -99,3 +99,13 @@
 void create_streams() {
   std::basic_iostream<char> bio(17);
 }
+
+// Make sure we don't mangle 'std' as 'St' here.
+namespace N {
+  namespace std {
+    struct A { void f(); };
+    
+    // CHECK: define void @_ZN1N3std1A1fEv
+    void A::f() { }
+  }
+}