diff --git a/include/os/osString.h b/include/os/osString.h
index 1b518f9b81..3a4ff18694 100644
--- a/include/os/osString.h
+++ b/include/os/osString.h
@@ -67,7 +67,7 @@ bool    taosMbsToUcs4(const char *mbs, size_t mbs_len, TdUcs4 *ucs4, int32_t ucs
 int32_t tasoUcs4Compare(TdUcs4 *f1_ucs4, TdUcs4 *f2_ucs4, int32_t bytes);
 TdUcs4* tasoUcs4Copy(TdUcs4 *target_ucs4, TdUcs4 *source_ucs4, int32_t len_ucs4);
 bool    taosValidateEncodec(const char *encodec);
-int32_t taosHexEncode(const char *src, char *dst, int32_t len);
+int32_t taosHexEncode(const unsigned char *src, char *dst, int32_t len);
 int32_t taosHexDecode(const char *src, char *dst, int32_t len);
 
 int32_t taosWcharWidth(TdWchar wchar);
diff --git a/source/os/src/osString.c b/source/os/src/osString.c
index e6904f1963..efa65fe191 100644
--- a/source/os/src/osString.c
+++ b/source/os/src/osString.c
@@ -196,7 +196,7 @@ int32_t taosUcs4len(TdUcs4 *ucs4) {
 }
 
 //dst buffer size should be at least 2*len + 1
-int32_t taosHexEncode(const char *src, char *dst, int32_t len) {
+int32_t taosHexEncode(const unsigned char *src, char *dst, int32_t len) {
   if (!dst) {
     return -1;
   }