diff -r d2516d66101a -r a000bafece09 src/Types.cpp
--- a/src/Types.cpp	Mon Jul 30 12:13:08 2012 -0700
+++ b/src/Types.cpp	Mon Jul 30 12:13:22 2012 -0700
@@ -45,6 +45,8 @@
     if (!type)
         return NULL;
 
+    assert(!tag || strcmp(tag->chars(), "_"));
+
     type->kind_ = PRIMITIVE;
     type->tag_ = tag;
     type->contained_ = NULL;