=== modified file 'src/font.c'
--- src/font.c	2014-04-05 19:30:36 +0000
+++ src/font.c	2014-05-18 05:37:43 +0000
@@ -3299,6 +3299,7 @@
   Lisp_Object entity, name;
 
   entity = font_find_for_lface (f, attrs, spec, -1);
+  eassert (NILP (entity) || FONT_ENTITY_P (entity));  
   if (NILP (entity))
     {
       /* No font is listed for SPEC, but each font-backend may have
@@ -3307,6 +3308,7 @@
       if (NILP (entity))
 	return Qnil;
     }
+  eassert (NILP (entity) || FONT_ENTITY_P (entity));
   /* Don't lose the original name that was put in initially.  We need
      it to re-apply the font when font parameters (like hinting or dpi) have
      changed.  */