Index: lib/Frontend/CompilerInstance.cpp
===================================================================
--- lib/Frontend/CompilerInstance.cpp
+++ lib/Frontend/CompilerInstance.cpp
@@ -1724,7 +1724,9 @@
     // module cache, we don't know how to rebuild modules.
     unsigned ARRFlags = Source == ModuleCache ?
                         ASTReader::ARR_OutOfDate | ASTReader::ARR_Missing :
-                        ASTReader::ARR_ConfigurationMismatch;
+                        Source == PrebuiltModulePath ?
+                            0 :
+                            ASTReader::ARR_ConfigurationMismatch;
     switch (ModuleManager->ReadAST(ModuleFileName,
                                    Source == PrebuiltModulePath
                                        ? serialization::MK_PrebuiltModule