diff --git a/lib/Lex/PPLexerChange.cpp b/lib/Lex/PPLexerChange.cpp
index 09b6076..1df4d21 100644
--- a/lib/Lex/PPLexerChange.cpp
+++ b/lib/Lex/PPLexerChange.cpp
@@ -173,10 +173,14 @@
       SrcMgr::CharacteristicKind FileType =
         SourceMgr.getFileCharacteristic(CurPPLexer->getFileID());
       
-      if (CurLexer)
+      if (CurLexer) {
+        // FIXME: Should we use the location of 'Result'?
         Callbacks->FileChanged(CurLexer->getSourceLocation(CurLexer->BufferPtr),
                                PPCallbacks::ExitFile, FileType);
-      // FIXME: Add callback support for PTHLexer.
+      }
+      else {
+        assert (0 && "FIXME: Add callback support for PTHLexer.");
+      }
     }
 
     // Client should lex another token.