diff --git a/ostd/string.hh b/ostd/string.hh
index dbc75d4..8f8a100 100644
--- a/ostd/string.hh
+++ b/ostd/string.hh
@@ -331,6 +331,7 @@ public:
     }
 
     void clear() {
+        if (!p_len) return;
         p_len = 0;
         *p_buf.first() = '\0';
     }