diff --git a/cmdline/CTACmdMain.cpp b/cmdline/CTACmdMain.cpp
index 0d731be96975eb381022ce22d4e7aed81f26a7cc..f82514042ed1874458486a0658c80f529bf227e4 100644
--- a/cmdline/CTACmdMain.cpp
+++ b/cmdline/CTACmdMain.cpp
@@ -145,7 +145,8 @@ int sendCommand(const int argc, const char **argv) {
     }
     if(bytesRead != 1) {
       throw std::runtime_error(std::string("Failed to read first byte from ") + cmdPath +
-        ": Expected to read exactly 1 byte, actually read " + std::to_string(bytesRead) + " bytes");
+        ": Expected to read exactly 1 byte, actually read " +
+        std::to_string((long long unsigned int)bytesRead) + " bytes");
     }
     rc = rc_char - '0';
   }