diff --git a/nemu/src/monitor/sdb/addrexp.y b/nemu/src/monitor/sdb/addrexp.y
index cd2e6c9..584e12e 100644
--- a/nemu/src/monitor/sdb/addrexp.y
+++ b/nemu/src/monitor/sdb/addrexp.y
@@ -32,6 +32,7 @@ input
 expression
     : number { $$ = $1; }
     | expression '=' '=' expression { $$ = ($1 == $3); }
+    | expression '!' '=' expression { $$ = ($1 == $3); }
     | expression '>' '=' expression { $$ = ($1 >= $3); }
     | expression '<' '=' expression { $$ = ($1 <= $3); }
     | expression '>' expression { $$ = ($1 > $3); }