diff --git a/Calendar/DesignEntity.py b/Calendar/DesignEntity.py
index dc2f874..a766a79 100644
--- a/Calendar/DesignEntity.py
+++ b/Calendar/DesignEntity.py
@@ -10,6 +10,11 @@ class DesignEntity (object):
 
     def __init__(self, size, mask=False, invert_mask=False, color_key=False):
         self.size = size
+        # Are dimensions >= 0?
+        for i in range(2):
+            if self.size[i] < 0:
+                self.size[i] = 0
+        
         self.pos = (0, 0)
         self.mask = mask
         self.invert_mask = invert_mask