# UNDF: UNDF-2026-000000964
--- a/apps/openmw/mwmechanics/pathgrid.cpp
+++ b/apps/openmw/mwmechanics/pathgrid.cpp
@@ -1,6 +1,7 @@
 #include "pathgrid.hpp"

 #include <algorithm>
+#include <unordered_set>
 #include <list>
 #include <set>

@@ -250,6 +251,7 @@

         std::list<size_t> openset;
         std::set<size_t> closedset;
+        std::unordered_set<size_t> opensetMembership;
         openset.push_back(start);
+        opensetMembership.insert(start);

         size_t current = start;
@@ -260,6 +262,7 @@
             current = openset.front(); // front has the lowest cost
             openset.pop_front();
+            opensetMembership.erase(current);

             if (current == goal)
                 break;
@@ -274,7 +277,7 @@
                     size_t dest = edge.index;
                     float tentativeG = gScore[current] + edge.cost;
-                    bool isInOpenSet = std::find(openset.begin(), openset.end(), dest) != openset.end();
+                    bool isInOpenSet = opensetMembership.count(dest) > 0;
                     if (!isInOpenSet || tentativeG < gScore[dest])
                     {
                         graphParent[dest] = current;
@@ -282,6 +285,7 @@
                         fScore[dest] = tentativeG + costAStar(mPathgrid->mPoints[dest], mPathgrid->mPoints[goal]);
                         if (!isInOpenSet)
                         {
+                            opensetMembership.insert(dest);
                             // add this edge to openset, lowest cost goes to the front
                             // TODO: if this causes performance problems a hash table may help
                             auto it = openset.begin();