diff --git a/clang/lib/Lex/HeaderSearch.cpp b/clang/lib/Lex/HeaderSearch.cpp
index d6b255f..f76d851 100644
--- a/clang/lib/Lex/HeaderSearch.cpp
+++ b/clang/lib/Lex/HeaderSearch.cpp
@@ -115,11 +115,13 @@
 std::string HeaderSearch::getModuleFileName(Module *Module) {
   const FileEntry *ModuleMap =
       getModuleMap().getModuleMapFileForUniquing(Module);
-  return getModuleFileName(Module->Name, ModuleMap->getName());
+  return getModuleFileName(Module->Name, ModuleMap->getName(),
+                           Module->IsSystem);
 }
 
 std::string HeaderSearch::getModuleFileName(StringRef ModuleName,
-                                            StringRef ModuleMapPath) {
+                                            StringRef ModuleMapPath,
+                                            bool IsSystem) {
   // If we don't have a module cache path, we can't do anything.
   if (ModuleCachePath.empty()) 
     return std::string();
@@ -147,6 +149,10 @@
     llvm::hash_code Hash =
         llvm::hash_combine(DirName.lower(), FileName.lower());
 
+    // Hash the IsSystem bit, since changing search paths can change whether a
+    // module is considered 'system' or not.
+    Hash = llvm::hash_combine(Hash, IsSystem);
+
     SmallString<128> HashStr;
     llvm::APInt(64, size_t(Hash)).toStringUnsigned(HashStr, /*Radix*/36);
     llvm::sys::path::append(Result, ModuleName + "-" + HashStr.str() + ".pcm");