diff --git a/debugger/debug.l b/debugger/debug.l
index 71b2215..7b8d278 100644
--- a/debugger/debug.l
+++ b/debugger/debug.l
@@ -1,4 +1,4 @@
-/*
+/* -*-C-*-
  * Lexical scanner for command line parsing
  *
  * Copyright 1993 Eric Youngdale
@@ -26,6 +26,8 @@
 
 #endif  /* DONT_USE_READLINE */
 
+#define YY_NO_UNPUT
+
 static int syntax_error;
 %}