diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 74e9fed..a37e1ce 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -2416,7 +2416,7 @@
 
   // Extend the signature with the module file extensions.
   const FrontendOptions &frontendOpts = getFrontendOpts();
-  for (auto ext : frontendOpts.ModuleFileExtensions) {
+  for (const auto &ext : frontendOpts.ModuleFileExtensions) {
     code = ext->hashExtension(code);
   }