diff --git a/nemu/tests/expr_test.c b/nemu/tests/expr_test.c
index 2a46ec8..a31dd8f 100644
--- a/nemu/tests/expr_test.c
+++ b/nemu/tests/expr_test.c
@@ -173,7 +173,7 @@ START_TEST(test_expr_plain_register) {
   // NOTE: need to fix this if want to support more arch
   buf[0] = '$';
   for (i = 1; i < 32; i++) {
-    ck_assert(strcpy(buf + 1, regs[i]));
+    ck_assert(strncpy(buf + 1, regs[i], 10));
     gpr(i) = i;
     yy_scan_string(buf);
     result = yyparse(&value);