diff --git a/src/ui/mucwin.c b/src/ui/mucwin.c
index d13a89f1..66919b95 100644
--- a/src/ui/mucwin.c
+++ b/src/ui/mucwin.c
@@ -560,6 +560,8 @@ mucwin_handle_affiliation_list(ProfMucWin *mucwin, const char *const affiliation
 void
 mucwin_show_affiliation_list(ProfMucWin *mucwin, muc_affiliation_t affiliation)
 {
+    assert(mucwin != NULL);
+
     ProfWin *window = (ProfWin*) mucwin;
     GSList *occupants = muc_occupants_by_affiliation(mucwin->roomjid, affiliation);