Index: optimize.c
===================================================================
--- optimize.c	(revision 366671)
+++ optimize.c	(working copy)
@@ -1269,9 +1269,10 @@
 
 	for (atom = 0; atom < N_ATOMS; ++atom)
 		if (last[atom] && !ATOMELEM(b->out_use, atom)) {
 			last[atom]->code = NOP;
 			opt_state->done = 0;
+			vstore(0, &b->val[atom], VAL_UNKNOWN, 0);
 		}
 }
 
 static void