--- src/sendmsg-window.c.orig	2019-10-09 13:28:23.000000000 -0700
+++ src/sendmsg-window.c	2020-03-25 00:22:31.000000000 -0700
@@ -6971,7 +6971,7 @@
     sw_buffer_signals_connect(bsmsg);
 
 #if HAVE_GTKSOURCEVIEW
-    source_buffer = GTK_SOURCE_BUFFER(gtk_text_view_get_buffer
+    source_buffer = (GtkSourceBuffer *) (gtk_text_view_get_buffer
                                       (GTK_TEXT_VIEW(bsmsg->text)));
     gtk_source_buffer_begin_not_undoable_action(source_buffer);
     gtk_source_buffer_end_not_undoable_action(source_buffer);