diff --git a/src/lib_json/json_tool.h b/src/lib_json/json_tool.h
index ec2b1f27f..d16d7b851 100644
--- a/src/lib_json/json_tool.h
+++ b/src/lib_json/json_tool.h
@@ -63,7 +63,7 @@ typedef char UIntToStringBuffer[uintToStringBufferSize];
 static inline void uintToString(LargestUInt value, char*& current) {
   *--current = 0;
   do {
-    *--current = static_cast<signed char>(value % 10U + static_cast<unsigned>('0'));
+    *--current = static_cast<char>(value % 10U + static_cast<unsigned>('0'));
     value /= 10;
   } while (value != 0);
 }