diff --git a/nemu/src/monitor/sdb/addrexp.l b/nemu/src/monitor/sdb/addrexp.l
index 9d6b263..6882a0b 100644
--- a/nemu/src/monitor/sdb/addrexp.l
+++ b/nemu/src/monitor/sdb/addrexp.l
@@ -2,6 +2,7 @@
     #include <isa.h>
     #include <addrexp.h>
     static bool success = false;
+    void yyerror(word_t *result, const char *err); 
 %}
 %option noyywrap
 
@@ -10,7 +11,7 @@
 $[a-zA-Z]{2,3}   {
     yylval = isa_reg_str2val(yytext + 1, &success);
     if(!success) {
-        printf("YYTEXT: %s", yytext);
+        yyerror(NULL, "Failed to convert reg to value");
         return YYerror;
     }
 }
diff --git a/nemu/tests/expr_test.c b/nemu/tests/expr_test.c
index 0042372..18f8435 100644
--- a/nemu/tests/expr_test.c
+++ b/nemu/tests/expr_test.c
@@ -219,7 +219,7 @@ int main(void) {
   s = expr_suite();
   sr = srunner_create(s);
 
-  srunner_run_all(sr, CK_VERBOSE);
+  srunner_run_all(sr, CK_NORMAL);
   number_failed = srunner_ntests_failed(sr);
   srunner_free(sr);