diff --git a/src/data/db/find.ts b/src/data/db/find.ts
index 398a936..8ca1f6c 100644
--- a/src/data/db/find.ts
+++ b/src/data/db/find.ts
@@ -1,6 +1,6 @@
 import { PrismaClient } from '@prisma/client';
 import { MessageI, RoomI } from 'discreetly-interfaces';
-import { ClaimCodeI, GateWayIdentityI } from '../../types/';
+import { ClaimCodeI, GateWayIdentityI, Jubmojis } from '../../types/';
 const prisma = new PrismaClient();
 
 /**
@@ -155,11 +155,15 @@ export async function findRoomWithMessageId(
 }
 
 export async function findAllJubmojiNullifiers() {
-  const jubmojiNullifiers = await prisma.gateWayIdentity.findMany({
+  const jubmojiNullifiers: Jubmojis[] = await prisma.gateWayIdentity.findMany({
     select: {
       jubmoji: true
     }
   })
+  const usedSigNullifiers: string[] = [];
 
-  return jubmojiNullifiers;
+  jubmojiNullifiers.forEach((nullifier) => {
+    usedSigNullifiers.push(...nullifier.jubmoji as string[]);
+  });
+  return usedSigNullifiers
 }
diff --git a/src/endpoints/gateways/jubmojis.ts b/src/endpoints/gateways/jubmojis.ts
index 526820d..3332a12 100644
--- a/src/endpoints/gateways/jubmojis.ts
+++ b/src/endpoints/gateways/jubmojis.ts
@@ -8,6 +8,7 @@ import { RoomI } from 'discreetly-interfaces';
 import { jubmojiVerifier } from '../../gateways/jubmojis/jubmoji';
 import { JubmojiRequestI } from '../../gateways/jubmojis/jubmoji.types';
 
+
 const router = express.Router();
 const prisma = new PrismaClient();
 
diff --git a/src/gateways/jubmojis/jubmoji.ts b/src/gateways/jubmojis/jubmoji.ts
index 517d018..b199236 100644
--- a/src/gateways/jubmojis/jubmoji.ts
+++ b/src/gateways/jubmojis/jubmoji.ts
@@ -13,6 +13,7 @@ import { VerificationResult, VerifyArgs, ZKP, ZKPPublicSignals } from './jubmoji
 import { hexToBigInt } from './utils';
 import vkey from './vkey';
 import { cardPubKeys } from './pubkeys';
+import { findAllJubmojiNullifiers } from '../../data/db';
 
 export async function jubmojiVerifier(serializedMembershipProof): Promise<VerificationResult> {
   const merkleRoot = await getMerkleRootFromCache(collectionPubKeys);
@@ -61,9 +62,12 @@ const verifyMembership = async ({
     return { verified: false };
   }
   // TODO! This is where we need to check and make sure someone can't join more than once
-  // if (usedSigNullifiers && usedSigNullifiers.includes(publicSignals.sigNullifier)) {
-  //   return { verified: false };
-  // }
+
+  const usedSigNullifiers: string[] = await findAllJubmojiNullifiers();
+
+  if (usedSigNullifiers && usedSigNullifiers.includes(String(publicSignals.sigNullifier))) {
+    return { verified: false };
+  }
   const verified = await verifyMembershipZKP(vkey, proof.zkp);
   if (!verified) {
     return { verified: false };
diff --git a/src/types/index.ts b/src/types/index.ts
index 7c096c3..ff11fab 100644
--- a/src/types/index.ts
+++ b/src/types/index.ts
@@ -67,3 +67,7 @@ export interface addRoomData {
   admin?: boolean;
   discordIds?: string[];
 }
+
+export interface Jubmojis {
+  jubmoji: any[];
+}