diff --git a/day16/sol.py b/day16/sol.py
index a888581..2a9a9cc 100644
--- a/day16/sol.py
+++ b/day16/sol.py
@@ -152,6 +152,10 @@ def solve():
             m -= 1
         return c
 
+    def worst2(node):
+        _, _, min1, min2, closed = node
+        return min(min1,min2) * pressure(closed)
+
     def is_goal2(node):
         _, _, min1, min2, closed = node
         return min1 == 0 and min2 == 0 or closed == all_open
@@ -209,7 +213,7 @@ def solve():
     minutes = 26
     start2 = (AA, AA, minutes, minutes, all_closed)
     info.clear()
-    c, _, path = astar.search(start2, is_goal2, neighbors2, heuristic2)
+    c, _, path = astar.search(start2, is_goal2, neighbors2, heuristic2, worst=worst2)
     print(c)
     print(max_pressure*minutes - c)
 
diff --git a/lib/astar.py b/lib/astar.py
index b6eed66..e1fa793 100644
--- a/lib/astar.py
+++ b/lib/astar.py
@@ -1,6 +1,6 @@
 from heapq import heappush, heappop
 
-def search(start, is_goal, neighbors, heuristic=None):
+def search(start, is_goal, neighbors, heuristic=None, worst=None):
     if heuristic == None:
         def heuristic(x):
             return 0
@@ -16,6 +16,8 @@ def search(start, is_goal, neighbors, heuristic=None):
         i += 1
         heappush(q, (heuristic(s), i, s, None))
     done = {}
+    if worst:
+        best_worst = min(worst(s) for s in start)
     while q:
         z, _, this, prev = heappop(q)
         if this in done:
@@ -41,8 +43,15 @@ def search(start, is_goal, neighbors, heuristic=None):
             c = cost_so_far + c
             if n not in done or c < done[n][0]:
                 h = heuristic(n)
-                if h is None:
-                    continue
+                if worst:
+                    if c+h > best_worst:
+                        # if the best possible cost for this node
+                        # is worse than the lowest worst-case cost we've seen
+                        # then don't even bother exploring it
+                        continue
+                    w = worst(n)
+                    if c+w < best_worst:
+                        best_worst = c+w
                 i += 1
                 heappush(q, (c+h, i, n, this))