diff -ur m4-1.4.5.orig/src/builtin.c m4-1.4.5/src/builtin.c
--- m4-1.4.5.orig/src/builtin.c	2006-07-14 22:15:46.000000000 +0200
+++ m4-1.4.5/src/builtin.c	2006-07-17 19:13:27.000000000 +0200
@@ -1657,7 +1657,7 @@
 	case '\0':
 	  M4ERROR ((warning_status, 0, "\
 Warning: trailing \\ ignored in replacement"));
-	  break;
+	  return;
 
 	default:
 	  obstack_1grow (obs, ch);