diff --git a/boxes/__init__.py b/boxes/__init__.py
index a0f441e..a9c6bd1 100755
--- a/boxes/__init__.py
+++ b/boxes/__init__.py
@@ -631,9 +631,9 @@ class Boxes:
         :param r: radius
 
         """
-        radius -= self.burn
-        if radius < 0:
-            radius = 1E-9
+        r -= self.burn
+        if r < 0:
+            r = 1E-9
         self.moveTo(x+r, y)
         self.ctx.arc(-r, 0, r, 0, 2*math.pi)