diff --git a/foundry.toml b/foundry.toml
index 2d58b0d..afb1497 100644
--- a/foundry.toml
+++ b/foundry.toml
@@ -15,7 +15,7 @@ quote_style = "double"
 tab_width = 4
 
 [fuzz]
-runs = 4096
-max_test_rejects = 262144
+runs = 64
+max_test_rejects = 1262144
 
 # See more config options https://github.com/foundry-rs/foundry/blob/master/crates/config/README.md#all-options
diff --git a/lib/core b/lib/core
index 2a5f6f0..feb15ec 160000
--- a/lib/core
+++ b/lib/core
@@ -1 +1 @@
-Subproject commit 2a5f6f0fcee9a8d0ace03c38c77a352c5e5f95ae
+Subproject commit feb15ec0b55e30b56b9595a8b9d8f179f173bb76
diff --git a/src/extensions/managers/keys/KeyManagerBLS.sol b/src/extensions/managers/keys/KeyManagerBLS.sol
index a4786db..fcbf182 100644
--- a/src/extensions/managers/keys/KeyManagerBLS.sol
+++ b/src/extensions/managers/keys/KeyManagerBLS.sol
@@ -184,10 +184,10 @@ abstract contract KeyManagerBLS is KeyManager, BLSSig {
         // remove current key from merkle tree and aggregated key when new key is zero else update
         aggregatedKey = aggregatedKey.plus(currentKey.negate());
         if (key.X == 0 && key.Y == 0) {
-            $._keyMerkle.update(bytes32(0), bytes32(currentKey.X), proof, index);
+            $._keyMerkle.remove(bytes32(currentKey.X), proof, index);
         } else {
             aggregatedKey = aggregatedKey.plus(key);
-            $._keyMerkle.update(bytes32(key.X), bytes32(prevKey.X), proof, index);
+            $._keyMerkle.update(bytes32(key.X), bytes32(prevKey.X), proof, index, false);
         }
 
         $._aggregatedKey.push(_now(), aggregatedKey.X);
diff --git a/src/libraries/Merkle.sol b/src/libraries/Merkle.sol
index 69c4ebc..837351c 100644
--- a/src/libraries/Merkle.sol
+++ b/src/libraries/Merkle.sol
@@ -7,7 +7,6 @@ pragma solidity ^0.8.25;
 
 uint256 constant TREE_DEPTH = 16;
 uint256 constant MAX_LEAVES = 2 ** TREE_DEPTH - 1;
-uint256 constant MASK = 0xfffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffe;
 
 /**
  * @title MerkleLib
@@ -19,10 +18,13 @@ library MerkleLib {
     using MerkleLib for Tree;
 
     event UpdateLeaf(uint256 index, bytes32 node);
+    event PopLeaf();
 
     error InvalidProof();
     error FullMerkleTree();
     error InvalidIndex();
+    error SameNodeUpdate();
+    error EmptyTree();
 
     /**
      * @notice Struct representing incremental merkle tree. Contains current
@@ -31,7 +33,7 @@ library MerkleLib {
      */
     struct Tree {
         bytes32[TREE_DEPTH] branch;
-        uint256 count;
+        bytes32[] leaves;
     }
 
     /**
@@ -41,21 +43,22 @@ library MerkleLib {
      *
      */
     function insert(Tree storage _tree, bytes32 _node) internal {
-        if (_tree.count >= MAX_LEAVES) {
+        uint256 _size = _tree.leaves.length;
+
+        if (_size >= MAX_LEAVES) {
             revert FullMerkleTree();
         }
 
-        emit UpdateLeaf(_tree.count, _node);
+        emit UpdateLeaf(_size, _node);
+        _tree.leaves.push(_node);
 
-        _tree.count += 1;
-        uint256 size = _tree.count;
         for (uint256 i = 0; i < TREE_DEPTH; i++) {
-            if ((size & 1) == 1) {
+            if ((_size & 1) == 0) {
                 _tree.branch[i] = _node;
                 return;
             }
             _node = keccak256(abi.encodePacked(_tree.branch[i], _node));
-            size /= 2;
+            _size >>= 1;
         }
         // As the loop should always end prematurely with the `return` statement,
         // this code should be unreachable. We assert `false` just to be safe.
@@ -65,12 +68,13 @@ library MerkleLib {
     function update(
         Tree storage _tree,
         bytes32 _node,
-        bytes32 _oldNode,
+        bytes32 _oldNode, // we could read from storage, but we already have to check the old node proof validity
         bytes32[TREE_DEPTH] memory _branch,
-        uint256 _index
+        uint256 _index,
+        bool isRemove
     ) internal {
-        if (_index >= _tree.count) {
-            revert InvalidIndex();
+        if (_node == _oldNode) {
+            revert SameNodeUpdate();
         }
 
         bytes32 _root = branchRoot(_oldNode, _branch, _index);
@@ -79,26 +83,62 @@ library MerkleLib {
             revert InvalidProof();
         }
 
+        uint256 size = _tree.leaves.length;
+        if (_index >= size) {
+            revert InvalidIndex();
+        }
+
+        if (isRemove) {
+            size--;
+        }
+
+        _tree.leaves[_index] = _node;
         emit UpdateLeaf(_index, _node);
 
-        uint256 lastIndex = _tree.count - 1;
         for (uint256 i = 0; i < TREE_DEPTH; i++) {
-            if ((lastIndex / 2 * 2) == _index) {
+            if ((size / 2 * 2) == _index) {
                 _tree.branch[i] = _node;
                 return;
             }
-            if (_index & 0x01 == 1) {
+            if ((_index & 1) == 1) {
                 _node = keccak256(abi.encodePacked(_branch[i], _node));
             } else {
                 _node = keccak256(abi.encodePacked(_node, _branch[i]));
             }
-            lastIndex /= 2;
-            _index /= 2;
+            size >>= 1;
+            _index >>= 1;
         }
 
         assert(false);
     }
 
+    function pop(
+        Tree storage _tree
+    ) internal {
+        _tree.leaves.pop();
+        uint256 size = _tree.leaves.length;
+        bytes32 _node = bytes32(0);
+        emit PopLeaf();
+
+        for (uint256 i = 0; i < TREE_DEPTH; i++) {
+            if ((size & 1) == 0) {
+                _tree.branch[i] = _node;
+                return;
+            }
+            _node = keccak256(abi.encodePacked(_tree.branch[i], _node));
+            size >>= 1;
+        }
+
+        assert(false);
+    }
+
+    function remove(Tree storage _tree, bytes32 _node, bytes32[TREE_DEPTH] memory _branch, uint256 _index) internal {
+        if (_index != _tree.leaves.length - 1) {
+            update(_tree, _tree.leaves[_tree.leaves.length - 1], _node, _branch, _index, true);
+        }
+        pop(_tree);
+    }
+
     /**
      * @notice Calculates and returns`_tree`'s current root
      * @return _current Calculated root of `_tree`
@@ -108,10 +148,10 @@ library MerkleLib {
         Tree storage _tree
     ) internal view returns (bytes32 _current) {
         bytes32[TREE_DEPTH] memory _zeroes = zeroHashes();
-        uint256 _index = _tree.count;
+        uint256 _size = _tree.leaves.length;
 
         for (uint256 i = 0; i < TREE_DEPTH; i++) {
-            uint256 _ithBit = (_index >> i) & 0x01;
+            uint256 _ithBit = (_size >> i) & 0x01;
             bytes32 _next = _tree.branch[i];
             if (_ithBit == 1) {
                 _current = keccak256(abi.encodePacked(_next, _current));
diff --git a/test/Merkle.t.sol b/test/Merkle.t.sol
index 0ef82ae..ea9780d 100644
--- a/test/Merkle.t.sol
+++ b/test/Merkle.t.sol
@@ -87,6 +87,8 @@ contract MerkleTest is Test {
     function testFuzzInsert(
         bytes32 node
     ) public {
+        vm.assume(node != bytes32(0));
+
         simpleMerkle.insert(node);
         fullMerkle.insert(node);
 
@@ -97,19 +99,51 @@ contract MerkleTest is Test {
         assertEq(simpleMerkle.root(), fullMerkle.root());
     }
 
-    function testFuzzUpdate(bytes32 oldNode, bytes32 newNode) public {
-        simpleMerkle.insert(oldNode);
-        fullMerkle.insert(oldNode);
+    function testFuzzUpdate(bytes32[8] memory _nodes, uint256 _index, bytes32 newNode) public {
+        vm.assume(_index < _nodes.length);
+        vm.assume(_nodes[_index] != bytes32(0));
+        vm.assume(newNode != _nodes[_index]);
 
-        bytes32[16] memory proof = fullMerkle.getProof(0);
+        for (uint256 i = 0; i < _nodes.length; i++) {
+            simpleMerkle.insert(_nodes[i]);
+            fullMerkle.insert(_nodes[i]);
+        }
 
-        simpleMerkle.update(newNode, oldNode, proof, 0);
-        fullMerkle.update(newNode, 0);
+        bytes32[16] memory proof = fullMerkle.getProof(_index);
+
+        fullMerkle.update(newNode, _index);
+        simpleMerkle.update(newNode, _nodes[_index], proof, _index);
 
         // Verify new node
-        proof = fullMerkle.getProof(0);
-        assertTrue(simpleMerkle.verify(newNode, proof, 0));
-        assertTrue(fullMerkle.verify(newNode, proof, 0));
+        // proof = fullMerkle.getProof(_index);
+        assertTrue(fullMerkle.verify(newNode, proof, _index));
+        assertTrue(simpleMerkle.verify(newNode, proof, _index));
         assertEq(simpleMerkle.root(), fullMerkle.root());
     }
+
+    function testFuzzRemove(bytes32[8] memory _nodes, uint256 _index) public {
+        vm.assume(_index < _nodes.length);
+        for (uint256 i = 0; i < _nodes.length; i++) {
+            vm.assume(_nodes[i] != bytes32(0));
+        }
+
+        for (uint256 i = 0; i < _nodes.length; i++) {
+            simpleMerkle.insert(_nodes[i]);
+            fullMerkle.insert(_nodes[i]);
+            assertEq(simpleMerkle.root(), fullMerkle.root());
+        }
+
+        bytes32[16] memory proof = fullMerkle.getProof(_index);
+        simpleMerkle.remove(_nodes[_index], proof, _index);
+        fullMerkle.remove(_index);
+        assertEq(simpleMerkle.root(), fullMerkle.root());
+
+        _nodes[_index] = _nodes[_nodes.length - 1];
+
+        for (uint256 i = 0; i < _nodes.length - 1; i++) {
+            proof = fullMerkle.getProof(i);
+            assertTrue(fullMerkle.verify(_nodes[i], proof, i));
+            assertTrue(simpleMerkle.verify(_nodes[i], proof, i));
+        }
+    }
 }
diff --git a/test/helpers/FullMerkle.sol b/test/helpers/FullMerkle.sol
index 51d0864..cfd6518 100644
--- a/test/helpers/FullMerkle.sol
+++ b/test/helpers/FullMerkle.sol
@@ -5,7 +5,6 @@ contract FullMerkle {
     uint256 public constant DEPTH = 16;
     bytes32[DEPTH] public zeroValues;
     mapping(uint256 => mapping(uint256 => bytes32)) public nodes;
-    bytes32[] public leaves;
     uint256 public currentLeafIndex;
 
     constructor() {
@@ -33,7 +32,6 @@ contract FullMerkle {
         require(currentLeafIndex < 2 ** DEPTH, "Tree is full");
 
         uint256 leafPos = currentLeafIndex;
-        leaves.push(_node);
         nodes[0][leafPos] = _node;
 
         _updatePath(leafPos);
@@ -41,24 +39,37 @@ contract FullMerkle {
     }
 
     function update(bytes32 _node, uint256 _index) public {
-        require(_index < leaves.length, "Leaf index out of bounds");
+        require(_index < currentLeafIndex, "Leaf index out of bounds");
 
-        leaves[_index] = _node;
         nodes[0][_index] = _node;
 
         _updatePath(_index);
     }
 
+    function pop() public {
+        require(currentLeafIndex > 0, "Tree is empty");
+
+        update(bytes32(0), currentLeafIndex - 1);
+        currentLeafIndex--;
+    }
+
+    function remove(
+        uint256 _index
+    ) public {
+        require(_index < currentLeafIndex, "Leaf index out of bounds");
+
+        update(nodes[0][currentLeafIndex - 1], _index);
+        pop();
+    }
+
     function root() public view returns (bytes32) {
         return nodes[DEPTH][0];
     }
 
     function getProof(
         uint256 _index
-    ) public view returns (bytes32[16] memory) {
-        require(_index < leaves.length, "Leaf index out of bounds");
-
-        bytes32[16] memory proof;
+    ) public view returns (bytes32[16] memory proof) {
+        require(_index < currentLeafIndex, "Leaf index out of bounds");
         uint256 currentIndex = _index;
 
         for (uint256 i = 0; i < DEPTH; i++) {
diff --git a/test/helpers/SimpleMerkle.sol b/test/helpers/SimpleMerkle.sol
index 6da119c..4d634df 100644
--- a/test/helpers/SimpleMerkle.sol
+++ b/test/helpers/SimpleMerkle.sol
@@ -15,18 +15,26 @@ contract SimpleMerkle {
     }
 
     function update(bytes32 _node, bytes32 _oldNode, bytes32[TREE_DEPTH] memory _proof, uint256 _index) external {
-        tree.update(_node, _oldNode, _proof, _index);
+        tree.update(_node, _oldNode, _proof, _index, false);
     }
 
     function verify(bytes32 _node, bytes32[TREE_DEPTH] memory _proof, uint256 _index) external view returns (bool) {
         return tree.root() == MerkleLib.branchRoot(_node, _proof, _index);
     }
 
+    function pop() external {
+        tree.pop();
+    }
+
+    function remove(bytes32 _node, bytes32[TREE_DEPTH] memory _proof, uint256 _index) external {
+        tree.remove(_node, _proof, _index);
+    }
+
     function root() external view returns (bytes32) {
         return tree.root();
     }
 
     function count() external view returns (uint256) {
-        return tree.count;
+        return tree.leaves.length;
     }
 }