diff --git a/HISTORY.MD b/HISTORY.MD
index 9a0ea71..25a9133 100644
--- a/HISTORY.MD
+++ b/HISTORY.MD
@@ -1,3 +1,7 @@
+0.4.3 /2020-03-17
+=================
+* Updated code to avoid duplicated subscriptions by adding a hash to subscription object
+
 0.4.2 / 2020-02-16
 ==================
 
diff --git a/logic/observer.js b/logic/observer.js
index ab4ac2d..6e7c53b 100644
--- a/logic/observer.js
+++ b/logic/observer.js
@@ -1,4 +1,5 @@
-const errors = require('../util/errors'),
+    const crypto = require ('crypto')
+    const errors = require('../util/errors'),
     TransactionWatcher = require('./transaction-watcher'),
     Notifier = require('./notifier'),
     storage = require('./storage'),
@@ -38,10 +39,21 @@ class Observer {
     }
 
     subscribe(subscriptionParams, user) {
-        //TODO: prevent duplicate subscriptions by checking subscription hash (fields "account", "asset_type" etc.)
-        //https://www.npmjs.com/package/farmhash
         return this.loadSubscriptions()
             .then(() => {
+                // Create hash in the subscription to avoid duplication
+    
+                let hashData = `${subscriptionParams.reaction_url} ${subscriptionParams.account} ${subscriptionParams.memo} ${subscriptionParams.operation_types} ${subscriptionParams.asset_code} ${subscriptionParams.asset_issuer} ${subscriptionParams.expires}`
+                let hash = crypto.createHash('md5').update(hashData).digest("hex").toString();
+                subscriptionParams.hash = hash
+
+                let subscription = this.subscriptions.find(s => s.hash == hash)
+
+                if(subscription){
+
+                    return subscription
+                }
+
                 if (this.getActiveSubscriptionsCount() >= config.maxActiveSubscriptions) {
                     return Promise.reject(errors.forbidden('Max active subscriptions exceeded.'))
                 }
diff --git a/logic/storage.js b/logic/storage.js
index 77e49cc..4367406 100644
--- a/logic/storage.js
+++ b/logic/storage.js
@@ -58,6 +58,19 @@ class Storage {
             })
     }
 
+    /**
+     * 
+     * @param {*} hash - the hash of the subscription
+     */
+
+    async fetchSubscriptioHash(hash){
+        this.provider.fetchSubscriptioHash(hash)
+        .then(subscription =>{
+            return subscription
+        }) 
+    } 
+
+
     /**
      * Load next notification from db
      * @param {*} subscriptionId - subscription id
@@ -208,6 +221,8 @@ class Storage {
             subscription.expires = expirationDate
         }
 
+        subscription.hash = subscriptionParams.hash
+
         return this.provider.saveSubscription(subscription)
     }
 
diff --git a/models/subscription-model.js b/models/subscription-model.js
index 524ee3d..86e35c5 100644
--- a/models/subscription-model.js
+++ b/models/subscription-model.js
@@ -67,6 +67,12 @@ class SubscriptionModel extends Model {
      * Cached notifications, associated with the subscription
      */
     notifications
+
+    /**
+     * Subscription hash to avoid duplicated subscriptions
+     */
+    hash
+
 }
 
 module.exports = SubscriptionModel
\ No newline at end of file
diff --git a/package.json b/package.json
index abb6b43..4cbd53c 100644
--- a/package.json
+++ b/package.json
@@ -2,7 +2,7 @@
   "name": "@stellar-expert/operations-notifier",
   "license": "MIT",
   "private": true,
-  "version": "0.4.2",
+  "version": "0.4.3",
   "author": "orbitlens<orbit.lens@stellar.expert>",
   "description": "Stellar operations observer and notifier.",
   "main": "app.js",
diff --git a/persistence-layer/mongodb-storage-provider/index.js b/persistence-layer/mongodb-storage-provider/index.js
index 6bc48e1..0d198c6 100644
--- a/persistence-layer/mongodb-storage-provider/index.js
+++ b/persistence-layer/mongodb-storage-provider/index.js
@@ -41,6 +41,10 @@ class MongoDBStorageProvider extends StorageProvider {
         return Subscription.findById(id)
     }
 
+    fetchSubscriptioHash(hash){
+        return Subscription.findOne({hash})
+    }
+
     fetchNextNotification(subscriptionId) {
         return Notification.findOne({subscriptions: toObjectId(subscriptionId)})
     }
diff --git a/persistence-layer/mongodb-storage-provider/models/subscription-db-model.js b/persistence-layer/mongodb-storage-provider/models/subscription-db-model.js
index c80d336..29d48d6 100644
--- a/persistence-layer/mongodb-storage-provider/models/subscription-db-model.js
+++ b/persistence-layer/mongodb-storage-provider/models/subscription-db-model.js
@@ -13,7 +13,8 @@ const subscriptionSchema = new Schema({
     reaction_url: {type: String},
     delivery_failures: {type: Number, default: 0},
     sent: {type: Number, default: 0},
-    expires: {type: Date}
+    expires: {type: Date},
+    hash:{type:String}
 },
 {
     timestamps: {createdAt: 'created', updatedAt: 'updated'}