diff --git a/day18/sol.py b/day18/sol.py
index f71ed65..780fd58 100644
--- a/day18/sol.py
+++ b/day18/sol.py
@@ -53,11 +53,10 @@ def flood(lava, border):
         x |= roll(a, 1, +1)
         x |= roll(a, 2, -1)
         x |= roll(a, 2, +1)
-        x = x & ~border
-        x = x & ~lava
-        if (a == x).all():
-            a |= border
+        x &= ~lava
+        b = a | x
+        if (a == b).all():
             return a
-        a = x
+        a = b
 
 solve()