# UNDF: UNDF-2026-000000018
--- a/src/BulletCollision/CollisionDispatch/btCollisionObject.h
+++ b/src/BulletCollision/CollisionDispatch/btCollisionObject.h
@@ -23,6 +23,7 @@ subject to the following restrictions:

 #include "LinearMath/btTransform.h"
 #include "LinearMath/btMotionState.h"
+#include "LinearMath/btHashMap.h"
 #include "LinearMath/btAlignedObjectArray.h"

@@ -115,7 +115,8 @@ class btCollisionObject
 {
 private:
-    btAlignedObjectArray<const btCollisionObject*> m_objectsWithoutCollisionCheck;
+    btAlignedObjectArray<const btCollisionObject*> m_objectsWithoutCollisionCheck;  // for serialization
+    btHashMap<btHashPtr, bool> m_ignoreSet;  // O(1) membership index

 public:
@@ -235,7 +237,7 @@ public:
     void setIgnoreCollisionCheck(const btCollisionObject* co, bool ignoreCollisionCheck)
     {
         if (ignoreCollisionCheck)
         {
-            //int index = m_objectsWithoutCollisionCheck.findLinearSearch(co);
-            //if (index == m_objectsWithoutCollisionCheck.size())
-            //{
+            if (!m_ignoreSet.find(btHashPtr(co)))
+            {
                 m_objectsWithoutCollisionCheck.push_back(co);
-            //}
+                m_ignoreSet.insert(btHashPtr(co), true);
+            }
         }
         else
         {
             m_objectsWithoutCollisionCheck.remove(co);
+            m_ignoreSet.remove(btHashPtr(co));
         }
         m_checkCollideWith = m_objectsWithoutCollisionCheck.size() > 0;
     }

@@ -266,10 +268,8 @@ public:
     virtual bool checkCollideWithOverride(const btCollisionObject* co) const
     {
-        int index = m_objectsWithoutCollisionCheck.findLinearSearch(co);  // O(N)
-        if (index < m_objectsWithoutCollisionCheck.size())
-        {
-            return false;
-        }
-        return true;
+        // O(1) hash lookup — replaces O(N) findLinearSearch
+        return !m_ignoreSet.find(btHashPtr(co));
     }