diff --git a/src/rln.ts b/src/rln.ts
index ce31e86..abc249d 100644
--- a/src/rln.ts
+++ b/src/rln.ts
@@ -26,6 +26,20 @@ function concatenate(...input: Uint8Array[]): Uint8Array {
   return result;
 }
 
+/**
+ * Transforms Uint8Array into BigInt
+ * @param array: Uint8Array
+ * @returns BigInt
+ */
+function buildBigIntFromUint8Array(array: Uint8Array): bigint {
+  const bigEndianArray = array.reverse();
+  // hack for Uint8Array.map that has Uint8Array -> Uint8Array definition that prevents from mapping to other types
+  const hexString = (bigEndianArray as unknown as number[])
+    .map((b) => b.toString(16).padStart(2, "0"))
+    .join();
+  return BigInt(`0x${hexString}`);
+}
+
 const stringEncoder = new TextEncoder();
 
 const DEPTH = 20;
@@ -59,13 +73,15 @@ export async function create(): Promise<RLNInstance> {
 export class MembershipKey {
   constructor(
     public readonly IDKey: Uint8Array,
-    public readonly IDCommitment: Uint8Array
+    public readonly IDCommitment: Uint8Array,
+    public readonly IDCommitmentBigInt: bigint
   ) {}
 
   static fromBytes(memKeys: Uint8Array): MembershipKey {
     const idKey = memKeys.subarray(0, 32);
     const idCommitment = memKeys.subarray(32);
-    return new MembershipKey(idKey, idCommitment);
+    const idCommitmentBitInt = buildBigIntFromUint8Array(idCommitment);
+    return new MembershipKey(idKey, idCommitment, idCommitmentBitInt);
   }
 }
 
diff --git a/src/rln_contract.ts b/src/rln_contract.ts
index b9dc36c..7ef0b9c 100644
--- a/src/rln_contract.ts
+++ b/src/rln_contract.ts
@@ -91,7 +91,7 @@ export class RLNContract {
     const membershipKey = await rlnInstance.generateSeededMembershipKey(
       signature
     );
-    const pubkey = ethers.BigNumber.from(membershipKey.IDCommitment);
+    const pubkey = ethers.BigNumber.from(membershipKey.IDCommitmentBigInt);
     const depositValue = await this.contract.MEMBERSHIP_DEPOSIT();
 
     const txRegisterResponse: ethers.ContractTransaction =