diff --git a/packages/protocols/src/utils.ts b/packages/protocols/src/utils.ts
index d7fcbec..89f8394 100644
--- a/packages/protocols/src/utils.ts
+++ b/packages/protocols/src/utils.ts
@@ -62,9 +62,15 @@ export function generateMerkleProof(
   zeroValue: StrBigInt,
   arity: number,
   leaves: StrBigInt[],
-  leafIndex: number
+  leaf: StrBigInt
 ): MerkleProof {
   const tree = generateMerkleTree(depth, zeroValue, arity, leaves)
 
+  const leafIndex = leaves.indexOf(BigInt(leaf))
+
+  if (leafIndex === -1) {
+    throw new Error("The leaf does not exists")
+  }
+
   return tree.createProof(leafIndex)
 }
diff --git a/packages/protocols/tests/rln.test.ts b/packages/protocols/tests/rln.test.ts
index d9eb15a..637df14 100644
--- a/packages/protocols/tests/rln.test.ts
+++ b/packages/protocols/tests/rln.test.ts
@@ -41,7 +41,7 @@ describe("RLN", () => {
       const epoch: string = genExternalNullifier("test-epoch")
       const rlnIdentifier = RLN.genIdentifier()
 
-      const merkleProof = generateMerkleProof(15, BigInt(0), 2, leaves, leaves.length - 1)
+      const merkleProof = generateMerkleProof(15, BigInt(0), 2, leaves, identityCommitment)
       const witness = RLN.genWitness(secretHash, merkleProof, epoch, signal, rlnIdentifier)
 
       expect(typeof witness).toBe("object")
@@ -61,7 +61,7 @@ describe("RLN", () => {
       const epoch = genExternalNullifier("test-epoch")
       const rlnIdentifier = RLN.genIdentifier()
 
-      const merkleProof = generateMerkleProof(15, BigInt(0), 2, leaves, leaves.length - 1)
+      const merkleProof = generateMerkleProof(15, BigInt(0), 2, leaves, identityCommitment)
       const witness = RLN.genWitness(secretHash, merkleProof, epoch, signal, rlnIdentifier)
 
       const [y, nullifier] = RLN.calculateOutput(secretHash, BigInt(epoch), rlnIdentifier, signalHash)
diff --git a/packages/protocols/tests/semaphore.test.ts b/packages/protocols/tests/semaphore.test.ts
index e96175a..373a6dc 100644
--- a/packages/protocols/tests/semaphore.test.ts
+++ b/packages/protocols/tests/semaphore.test.ts
@@ -26,7 +26,7 @@ describe("Semaphore", () => {
       const leaves = [BigInt(3), BigInt(2), identityCommitment, BigInt(4)]
       const signal = "0x111"
 
-      const merkleProof = generateMerkleProof(20, BigInt(0), 5, leaves, 2)
+      const merkleProof = generateMerkleProof(20, BigInt(0), 5, leaves, identityCommitment)
 
       const witness = Semaphore.genWitness(
         identity.getTrapdoor(),
@@ -47,7 +47,7 @@ describe("Semaphore", () => {
       const leaves = [BigInt(3), BigInt(2), identityCommitment, BigInt(4)]
       const signal = "0x111"
 
-      const merkleProof = generateMerkleProof(20, BigInt(0), 5, leaves, 2)
+      const merkleProof = generateMerkleProof(20, BigInt(0), 5, leaves, identityCommitment)
 
       const witness = Semaphore.genWitness(
         identity.getTrapdoor(),