diff --git a/rpi/roy-test.py b/rpi/roy-test.py
index 05b0d5e..529e1c3 100644
--- a/rpi/roy-test.py
+++ b/rpi/roy-test.py
@@ -25,7 +25,7 @@ image.thumbnail((matrix.width, matrix.height), Image.ANTIALIAS)
 
 
 def updateScreen():
-    global color
+    global color, matrix, offscreen_canvas
     if(color == 1):
         offscreen_canvas.Fill(255,255,255)
     elif(color == 0):