Index: compilers/imcc/imcc.l
===================================================================
--- compilers/imcc/imcc.l	(revision 35299)
+++ compilers/imcc/imcc.l	(working copy)
@@ -618,6 +618,12 @@
         return REG;
     }
 
+<emit,INITIAL>"cpu_ret" {
+        Parrot_ex_throw_from_c_args(IMCC_INFO(interp), NULL, 1,
+            "cpu_ret opcode is reserved and should never be used directly");
+    }
+            
+
 <emit,INITIAL>{ID} {
         if (!is_def) {
             SymReg *r = find_sym(interp, yytext);