diff --git a/nemu/src/monitor/sdb/addrexp.y b/nemu/src/monitor/sdb/addrexp.y
index 815c7b5..9e1f2bf 100644
--- a/nemu/src/monitor/sdb/addrexp.y
+++ b/nemu/src/monitor/sdb/addrexp.y
@@ -44,7 +44,7 @@ expression
     | '(' expression ')' { $$ = $2; }
 
 number
-    : REGISTER { $$ = $1; }
+    : REGISTER
     | NUMBER 
     | HEX_NUMBER