diff --git a/libraries/AP_OSD/AP_OSD_ParamSetting.cpp b/libraries/AP_OSD/AP_OSD_ParamSetting.cpp
index 3f06082204..95476abd8f 100644
--- a/libraries/AP_OSD/AP_OSD_ParamSetting.cpp
+++ b/libraries/AP_OSD/AP_OSD_ParamSetting.cpp
@@ -119,7 +119,7 @@ static const char* SERIAL_PROTOCOL_VALUES[] = {
     "GEN", "WNCH", "MSP", "DJI", "AIRSPD", "ADSB", "AHRS", "AUDIO", "FETTEC", "TORQ",
     "AIS", "CD_ESC", "MSP_DP", "MAV_HL", "TRAMP", "DDS"
 };
-static_assert(AP_SerialManager::SerialProtocol_NumProtocols == ARRAY_SIZE(SERIAL_PROTOCOL_VALUES));
+static_assert(AP_SerialManager::SerialProtocol_NumProtocols == ARRAY_SIZE(SERIAL_PROTOCOL_VALUES), "Wrong size SerialProtocol_NumProtocols");
 
 static const char* SERVO_FUNCTIONS[] = {
     "NONE", "RCPASS", "FLAP", "FLAP_AUTO", "AIL", "", "MNT_PAN", "MNT_TLT", "MNT_RLL", "MNT_OPEN",