work-around for older gtkmm versions

diff --git a/src/ui/previewholder.cpp b/src/ui/previewholder.cpp
index f809ba44c0526423728eb77b9a04e5dd8c19df82..b89e68adceabc145164e38132e21d4123266cea7 100644 (file)
--- a/src/ui/previewholder.cpp
+++ b/src/ui/previewholder.cpp
@@ -206,7 +206,7 @@ void PreviewHolder::calcGridSize( const Gtk::Widget* thing, int itemCount, int&
         }
 
         Gtk::Requisition req2;
-        thing->size_request(req2);
+        const_cast<Gtk::Widget*>(thing)->size_request(req2);
 
         int h2 = req.height / req2.height;
         int w2 = req.width / req2.width;