diff --git a/tests/test-mstring.c b/tests/test-mstring.c
index 0e1ed464..92339db0 100644
--- a/tests/test-mstring.c
+++ b/tests/test-mstring.c
@@ -656,7 +656,7 @@ static void test_int(void)
   assert(string_equal_str_p(s, "4294967295"));
 
   for(int i = -10000; i <= 10000; i++) {
-    sprintf(buffer, "%d", i);
+    snprintf(buffer, sizeof buffer, "%d", i);
     string_set_si(s, i);
     assert(string_equal_str_p(s, buffer));
   }