diff --git a/Source/cmSystemTools.cxx b/Source/cmSystemTools.cxx
index 49f5bd079e..cd7fa08e58 100644
--- a/Source/cmSystemTools.cxx
+++ b/Source/cmSystemTools.cxx
@@ -4165,7 +4165,7 @@ std::string cmSystemTools::EncodeURL(std::string const& in, bool escapeSlashes)
       case ' ':
       case '=':
       case '%':
-        snprintf(hexCh, sizeof(hexCh), "%%%02X", static_cast<int>(c));
+        snprintf(hexCh, sizeof(hexCh), "%%%02X", static_cast<unsigned int>(c));
         break;
       case '/':
         if (escapeSlashes) {