diff --git a/Utilities/cmjsoncpp/src/lib_json/json_reader.cpp b/Utilities/cmjsoncpp/src/lib_json/json_reader.cpp
index 41896a7f0..7b338285c 100644
--- a/Utilities/cmjsoncpp/src/lib_json/json_reader.cpp
+++ b/Utilities/cmjsoncpp/src/lib_json/json_reader.cpp
@@ -529,7 +529,7 @@ bool Reader::decodeNumber(Token& token, Value& decoded) {
       return addError("'" + std::string(token.start_, token.end_) +
                           "' is not a number.",
                       token);
-    Value::UInt digit(c - '0');
+    Value::UInt digit(static_cast<Value::UInt>(c - '0'));
     if (value >= threshold) {
       // We've hit or exceeded the max value divided by 10 (rounded down). If
       // a) we've only just touched the limit, b) this is the last digit, and