diff --git a/effects.py b/effects.py
index c7d3c21..133f030 100644
--- a/effects.py
+++ b/effects.py
@@ -324,6 +324,9 @@ class LetterTest(Effect):
     Minimum wall size: 8 x 8.
     """
     def run(self):
+        if self.wall.width < 8 or self.wall.height < 8:
+            return
+
         color = random.random()
         foreground = (color, 1, 1)
         # Make the foreground and background complementary colors.