Provided is a protective cap for mounting on a plug connector housing in order to protect the plug connector housing and plug connector modules received in the plug connector housing from environmental influences such as dirt, dust and moisture. At least one receptacle in the form of a rubber nipple is provided in a plug-in side of the protective cap, which receptacle is suitable for mechanical contact-making with a plug connector module received in the plug connector housing. The mechanical connection between the protective cap and plug connector module ensures that the plug connector module is protected from damage during transport and secured against loss and falling out when the protective cap is released. Moreover, the plug connector module can be removed, together with the protective cap, from the plug connector housing.