diff --git a/lib/Frontend/RewriteMacros.cpp b/lib/Frontend/RewriteMacros.cpp
index 954e8e2..4ffb297 100644
--- a/lib/Frontend/RewriteMacros.cpp
+++ b/lib/Frontend/RewriteMacros.cpp
@@ -101,7 +101,8 @@
 
 
   // Get the first preprocessing token.
-  PP.EnterMainSourceFile();
+  if (PP.EnterMainSourceFile())
+    return;
   Token PPTok;
   PP.Lex(PPTok);