diff --git a/nemu/src/monitor/sdb/addrexp.l b/nemu/src/monitor/sdb/addrexp.l
index 255c4ce..d702c5a 100644
--- a/nemu/src/monitor/sdb/addrexp.l
+++ b/nemu/src/monitor/sdb/addrexp.l
@@ -10,7 +10,7 @@
 
 0[xX][0-9a-fA-F]+ { yylval = strtoul(yytext, NULL, 16); return HEX_NUMBER; }
 [0-9]+            { yylval = strtoul(yytext, NULL, 10); return NUMBER; }
-${1,2}[a-zA-Z]{2,3}    {
+$[asgprt$][0-9pa][0-9]?    {
     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 eb1cf67..f0db0d5 100644
--- a/nemu/tests/expr_test.c
+++ b/nemu/tests/expr_test.c
@@ -175,7 +175,6 @@ START_TEST(test_expr_plain_register) {
   for (i = 1; i < 32; i++) {
     ck_assert(strcpy(buf + 1, regs[i]));
     gpr(i) = i;
-    printf("%d: %s\n", i, buf);
     yy_scan_string(buf);
     result = yyparse(&value);
     ck_assert_msg(result == 0, "expr = %s\n", buf);