diff --git a/mach/proto/as/comm6.c b/mach/proto/as/comm6.c
index a7925149..5900c258 100644
--- a/mach/proto/as/comm6.c
+++ b/mach/proto/as/comm6.c
@@ -90,7 +90,7 @@ register item_t *ip;
 	if (store(ip, (valu_t) DOTVAL) == 0)
 		return;
 #ifdef THREE_PASS
-	assert(pass != PASS_2 || oldval - ip->i_valu == DOTGAIN);
+	assert(pass != PASS_2 || oldval - (ADDR_T) ip->i_valu == DOTGAIN);
 #endif
 }