diff --git a/others/planck.py b/others/planck.py
index 7b2f0c3..553840d 100644
--- a/others/planck.py
+++ b/others/planck.py
@@ -33,7 +33,7 @@ rp = (MEMORY_SIZE - STACK_SIZE) * CELL
 ip = 0
 np = 0
 
-ALIGN_MASK = CELL - 1
+ALIGN_MASK = ~(CELL - 1)
 def aligned(n):
     return (n + CELLm1) & ALIGN_MASK