diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index a8d80a0..d179cef 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -372,6 +372,9 @@
 void CompilerInstance::createPreprocessor(TranslationUnitKind TUKind) {
   const PreprocessorOptions &PPOpts = getPreprocessorOpts();
 
+  // The module manager holds a reference to the old prepreocssor (if any).
+  ModuleManager.reset();
+
   // Create a PTH manager if we are using some form of a token cache.
   PTHManager *PTHMgr = nullptr;
   if (!PPOpts.TokenCache.empty())