Deprecated function message

I'm not sure whether this issue is related to the module or is caused by the php-version or something completely different, because I found several similar issues that were posted in other modules (see: https://www.google.com/search?ie=UTF-8&q=Deprecated+function%3A+Call-tim...() ).

Deprecated function: Call-time pass-by-reference has been deprecated in require_once() (Zeile 29 von [project]/sites/all/modules/pickem/pickem.module)

The corresponding line in the file "pickem.module" is: "require_once 'pickem.inc';"

The message seems not to cause any functional problems in the pickem-module.

It doesn't matter what module version (stable or dev) or what php-version (5.29 or 5.3) I'm using.

Thanks in advance.