diff --git a/nemu/tests/expr_test.c b/nemu/tests/expr_test.c
index d95c737..d6f308b 100644
--- a/nemu/tests/expr_test.c
+++ b/nemu/tests/expr_test.c
@@ -181,7 +181,7 @@ START_TEST(test_expr_plain_register) {
     yylex_destroy();
 
     ck_assert(value == i);
-    for (j = 1; j < 5; i++) {
+    for (j = 1; j < 5; j++) {
       buf[i] = '\0';
     }
   }