diff --git a/nemu/src/monitor/sdb/watchpoint.c b/nemu/src/monitor/sdb/watchpoint.c
index 7b3dee0..e8cec07 100644
--- a/nemu/src/monitor/sdb/watchpoint.c
+++ b/nemu/src/monitor/sdb/watchpoint.c
@@ -61,11 +61,11 @@ bool wp_check_hit(void) {
   return res;
 }
 
-static WP* del_wp(WP* head, WP* pos) {
-  for (WP** i = &head; (*i) != NULL && (*i)->next != NULL; i = (WP**)*i) {
+static WP* del_wp(WP** head, WP* pos) {
+  for (WP** i = head; (*i) != NULL && (*i)->next != NULL; i = (WP**)*i) {
     if ((**i).NO == pos->NO) {
       WP* res = *i;
-      *i = (**i).next;
+      *i = (*i)->next;
       return res;
     }
   }
@@ -87,7 +87,7 @@ WP* new_wp(char* _expr, int len) {
   if (!success) {
     return NULL;
   }
-  WP* wp = del_wp(free_, free_);
+  WP* wp = del_wp(&free_, free_);
   if (wp == NULL) {
     assert(0);
   }
@@ -108,7 +108,7 @@ WP* get_wp(int NO) {
 }
 
 void free_wp(WP *_wp) {
-  WP* wp = del_wp(head, _wp);
+  WP* wp = del_wp(&head, _wp);
   wp->next = free_;
   free_ = wp;
   wp->expr[0] = '\0';