diff --git a/contracts/MerkleTreeWithHistory.sol b/contracts/MerkleTreeWithHistory.sol
index a374bff..74a4bc3 100644
--- a/contracts/MerkleTreeWithHistory.sol
+++ b/contracts/MerkleTreeWithHistory.sol
@@ -58,7 +58,7 @@ contract MerkleTreeWithHistory {
 
   function _insert(uint256 leaf) internal {
     uint32 current_index = next_index;
-    require(current_index != 2**(levels - 1), "Merkle tree is full");
+    require(current_index != 2**levels, "Merkle tree is full");
     next_index += 1;
     uint256 current_level_hash = leaf;
     uint256 left;
diff --git a/test/MerkleTreeWithHistory.test.js b/test/MerkleTreeWithHistory.test.js
index 742c00c..730c25c 100644
--- a/test/MerkleTreeWithHistory.test.js
+++ b/test/MerkleTreeWithHistory.test.js
@@ -180,7 +180,7 @@ contract('MerkleTreeWithHistory', accounts => {
       zeroValue = 1337
       merkleTreeWithHistory = await MerkleTreeWithHistory.new(levels, zeroValue)
 
-      for (let i = 0; i < 2**(levels - 1); i++) {
+      for (let i = 0; i < 2**levels; i++) {
         await merkleTreeWithHistory.insert(i+42).should.be.fulfilled
       }