diff --git a/nemu/src/monitor/sdb/addrexp.l b/nemu/src/monitor/sdb/addrexp.l
index 124b8a3..274f3ce 100644
--- a/nemu/src/monitor/sdb/addrexp.l
+++ b/nemu/src/monitor/sdb/addrexp.l
@@ -11,7 +11,6 @@
 0[xX][0-9a-fA-F]+ { yylval = strtoul(yytext, NULL, 16); return HEX_NUMBER; }
 [0-9]+            { yylval = strtoul(yytext, NULL, 10); return NUMBER; }
 $[a-zA-Z]{2,3}    {
-    puts(yytext);
     yylval = isa_reg_str2val(yytext + 1, &success);
     if(!success) {
         yyerror(NULL, "Failed to convert reg to value");
diff --git a/nemu/tests/expr_test.c b/nemu/tests/expr_test.c
index 18f8435..8ffbc6a 100644
--- a/nemu/tests/expr_test.c
+++ b/nemu/tests/expr_test.c
@@ -175,6 +175,12 @@ START_TEST(test_expr_plain_register) {
     ck_assert(strcpy(buf + 1, regs[i]));
     gpr(i) = i;
   }
+  yy_scan_string(buf);
+  uint32_t value;
+  ck_assert(!yyparse(&value));
+  yylex_destroy();
+
+  ck_assert(value == i);
   for (i = 1; i < 5; i++) {
     buf[i] = '\0';
   }