diff --git a/api/i_cmdparser.hpp b/api/i_cmdparser.hpp
index 54c3b47..d09ac90 100644
--- a/api/i_cmdparser.hpp
+++ b/api/i_cmdparser.hpp
@@ -42,7 +42,7 @@ class ICmdParserACK {
   }
 
   int32_t *getAck(int index) {
-    if (index < 0 || index >= sizeof(rawdata) / 4) {
+    if (index < 0 || index >= (int32_t)(sizeof(rawdata) / 4)) {
       return nullptr;
     }
     return (int32_t *)rawdata + index;
@@ -64,4 +64,4 @@ class ICmdParser {
   virtual void regCMD(const char *cmdname, const char *helpinfo, int paraNum, ICmdFunction_t cmdimpl) = 0;
 };
 
-}  // namespace iflytop
\ No newline at end of file
+}  // namespace iflytop