Beautifier with uncrustify cannot handle objective-c string literals

If uncrustify is called on an objective-c++ file (xxx.mm) with string literals like

[tf setStringValue:@"XXX123XXX"];

I get the message "Error in Beautifier: /opt/local/bin/uncrustify: stdin:115 Garbage in col 21: 40"

If uncrustify is called on the file via shell and the same configuration everything is fine.