diff --git a/tests/src/TecDummy.cc b/tests/src/TecDummy.cc
index ed1fe4b7fcbb76a0fc07135ca03c6ec867854e47..aad297274d9d31247e36260e24050fc958acffa7 100644
--- a/tests/src/TecDummy.cc
+++ b/tests/src/TecDummy.cc
@@ -147,7 +147,7 @@ std::string TecDummy::processFrame(const std::string& command) {
     result = "!" + parsedFrame[TecFramePart::ADDRESS] + parsedFrame[TecFramePart::SEQUENCE];
     result += "+"; // marks the error
     std::stringstream ss;
-    ss << std::hex << std::setw(2) << std::setfill('0') << static_cast<int>(errorFlags[parameterId]);
+    ss << std::hex << std::setw(2) << std::setfill('0') << std::uppercase << static_cast<int>(errorFlags[parameterId]);
     result += ss.str();
     result += getCrc(result);
   }