diff --git a/lib/Frontend/PCHReader.cpp b/lib/Frontend/PCHReader.cpp
index 9970eb2..0407ed8 100644
--- a/lib/Frontend/PCHReader.cpp
+++ b/lib/Frontend/PCHReader.cpp
@@ -2563,6 +2563,7 @@
   }
 
   Index -= pch::NUM_PREDEF_TYPE_IDS;
+  assert(Index < TypesLoaded.size() && "Type index out-of-range");
   if (!TypesLoaded[Index])
     TypesLoaded[Index] = ReadTypeRecord(TypeOffsets[Index]).getTypePtr();