Index: typeck.c
===================================================================
--- typeck.c	(revision 120428)
+++ typeck.c	(working copy)
@@ -1121,22 +1121,22 @@ comptypes (tree t1, tree t2, int strict)
 	      /* The two types are structurally equivalent, but their
 		 canonical types were different. This is a failure of the
 		 canonical type propagation code.*/
-	      warning(0,
-		      "canonical types differ for identical types %T and %T", 
-		      t1, t2);
+	      error ("canonical types differ for identical types %T and %T", 
+		     t1, t2);
 	      debug_tree (t1);
 	      debug_tree (t2);
+	      gcc_unreachable ();
 	    }
 	  else if (!result && TYPE_CANONICAL (t1) == TYPE_CANONICAL (t2))
 	    {
 	      /* Two types are structurally different, but the canonical
 		 types are the same. This means we were over-eager in
 		 assigning canonical types. */
-	      warning (0, 
-		       "same canonical type node for different types %T and %T",
-		       t1, t2);
+	      error ("same canonical type node for different types %T and %T",
+		     t1, t2);
 	      debug_tree (t1);
 	      debug_tree (t2);
+	      gcc_unreachable ();
 	    }
 	  
 	  return result;