Index: gtkhid-cairo.c
===================================================================
--- gtkhid-cairo.c	(revision 17247)
+++ gtkhid-cairo.c	(revision 17248)
@@ -766,6 +766,8 @@
 		cap = CAIRO_LINE_CAP_SQUARE;
 		join = CAIRO_LINE_JOIN_MITER;
 		break;
+	default:
+		assert(!"unhandled cap");
 	}
 	gc->cap = cap;
 	gc->join = join;