diff --git a/nemu/tests/expr_test.c b/nemu/tests/expr_test.c
index df65db0..59ed3d3 100644
--- a/nemu/tests/expr_test.c
+++ b/nemu/tests/expr_test.c
@@ -173,7 +173,7 @@ START_TEST(test_expr_plain_register) {
   buf[0] = '$';
   for (i = 0; i < 32; i++) {
     ck_assert(strcpy(buf + 1, regs[i]));
-    puts(buf);
+    fputs(buf, stderr);
     gpr(i) = i;
   }
   yy_scan_string(buf);