diff --git a/buggy.py b/buggy.py
--- a/buggy.py
+++ b/buggy.py
@@ -17,7 +17,7 @@
         diagonal[1].append(a)
     if (
         (len(horizontal[row]) == N)
-        or (len(vertical[col - 1]) == N)
+        or (len(vertical[col]) == N)
         or (len(diagonal[0])) == N
         or (len(diagonal[1])) == N
     ):
