diff --git a/httplib.h b/httplib.h
index 8eb86a3..cc54ff8 100644
--- a/httplib.h
+++ b/httplib.h
@@ -4629,7 +4629,7 @@ inline std::string sha1(const std::string &input) {
   // Pre-processing: adding padding bits
   std::string msg = input;
   uint64_t original_bit_len = static_cast<uint64_t>(msg.size()) * 8;
-  msg.push_back(static_cast<char>(0x80));
+  msg.push_back(static_cast<char>(0x80u));
   while (msg.size() % 64 != 56) {
     msg.push_back(0);
   }