diff --git a/Makefile b/Makefile
index f9b1dd0..1a9a9a5 100644
--- a/Makefile
+++ b/Makefile
@@ -9,4 +9,4 @@ schema.png:
 	dot -Tpng -o $@ $< 
 
 clean:
-	rm *.png
+	rm $(PNGS)