diff --git a/Lib/turtle.py b/Lib/turtle.py
index 465d6e065d1..c9e88d9dd12 100644
--- a/Lib/turtle.py
+++ b/Lib/turtle.py
@@ -2594,7 +2594,7 @@ class RawTurtle(TPen, TNavigator):
         Example (for a Turtle instance named turtle):
         >>> turtle.setundobuffer(42)
         """
-        if size is None:
+        if size is None or size <= 0:
             self.undobuffer = None
         else:
             self.undobuffer = Tbuffer(size)