diff --git a/boxes/generators/flexbox4.py b/boxes/generators/flexbox4.py
index 8ed6d9d..899b8e5 100644
--- a/boxes/generators/flexbox4.py
+++ b/boxes/generators/flexbox4.py
@@ -69,7 +69,7 @@ class FlexBox(Boxes):
         self.corner(90)
 
     def render(self):
-        self.radius = self.radius or min(x, y)/2.0
+        self.radius = self.radius or min(self.x, self.y)/2.0
         self.c4 = c4 = math.pi * self.radius * 0.5
         self.latchsize = 8*self.thickness