diff --git a/src/ngamsCore/ngamsLib/ngamsDbNgasSubscribers.py b/src/ngamsCore/ngamsLib/ngamsDbNgasSubscribers.py
index 6bc39322..cbb0a68d 100644
--- a/src/ngamsCore/ngamsLib/ngamsDbNgasSubscribers.py
+++ b/src/ngamsCore/ngamsLib/ngamsDbNgasSubscribers.py
@@ -37,6 +37,7 @@
 
 from . import ngamsDbCore
 from .ngamsCore import fromiso8601
+from .ngamsSubscriber import ngamsSubscriber
 
 
 class ngamsDbNgasSubscribers(ngamsDbCore.ngamsDbCore):
@@ -132,6 +133,11 @@ def _getSubscriberInfo(self, tx, subscrId=None, hostId=None, portNo=-1):
 
 
     def insertSubscriberEntry(self, sub_obj):
+        """
+        Inserts the new subscription object into the NGAS subscription table.
+        If an object with the same subscription ID exists, its contents are
+        returned; otherwise the given object is returned.
+        """
 
         hostId = sub_obj.getHostId()
         portNo = sub_obj.getPortNo()
@@ -157,8 +163,15 @@ def insertSubscriberEntry(self, sub_obj):
                 filterPlugIn, filterPlugInPars, \
                 lastFileIngDate, concurrent_threads)
 
-        self.query2(sql, args = vals)
-        self.triggerEvents()
+        # If a subscriber with the given ID already exists return that
+        with self.transaction() as tx:
+            existing_sub = self._getSubscriberInfo(tx, subscrId=subscrId)
+            if existing_sub:
+                sub_obj = ngamsSubscriber().unpackSqlResult(existing_sub[0])
+            else:
+                tx.execute(sql, vals)
+                self.triggerEvents()
+        return sub_obj
 
 
     def updateSubscriberEntry(self, sub_obj):
diff --git a/src/ngamsServer/ngamsServer/commands/subscribe.py b/src/ngamsServer/ngamsServer/commands/subscribe.py
index d733bbac..0b00d460 100644
--- a/src/ngamsServer/ngamsServer/commands/subscribe.py
+++ b/src/ngamsServer/ngamsServer/commands/subscribe.py
@@ -52,10 +52,16 @@ def addSubscriber(srvObj, subscrObj):
 
     Returns:     Void.
     """
-    srvObj.getDb().insertSubscriberEntry(subscrObj)
-    #subscrObj.write(srvObj.getDb())
-
-    srvObj.registerSubscriber(subscrObj)
+    subscr_in_db = srvObj.getDb().insertSubscriberEntry(subscrObj)
+    if subscr_in_db is subscrObj:
+        srvObj.registerSubscriber(subscrObj)
+        # Trigger the Data Susbcription Thread to make it check if there are
+        # files to deliver to the new Subscriber.
+        srvObj.addSubscriptionInfo([], [subscrObj]).triggerSubscriptionThread()
+    elif subscr_in_db == subscrObj:
+        return 'equal'
+    else:
+        return 'unequal'
 
 
 def handleCmd(srvObj,
@@ -137,10 +143,10 @@ def handleCmd(srvObj,
             subscrObj.setLastFileIngDate(lastIngDate)
 
     # Register the Subscriber.
-    addSubscriber(srvObj, subscrObj)
-
-    # Trigger the Data Susbcription Thread to make it check if there are
-    # files to deliver to the new Subscriber.
-    srvObj.addSubscriptionInfo([], [subscrObj]).triggerSubscriptionThread()
+    existence_test = addSubscriber(srvObj, subscrObj)
+    if existence_test == 'equal':
+        return 201, "Identical subscription with ID '%s' existed" % (id,)
+    elif existence_test == 'unequal':
+        return 409, "Different subscription with ID '%s' existed" % (id,)
 
     return "Handled SUBSCRIBE command"
diff --git a/test/test_subscription.py b/test/test_subscription.py
index b92461de..40e26b8a 100644
--- a/test/test_subscription.py
+++ b/test/test_subscription.py
@@ -42,8 +42,8 @@
 import requests
 import trustme
 
-from ngamsLib import ngamsHttpUtils, ngamsSubscriber
-from ngamsLib.ngamsCore import getHostName
+from ngamsLib import ngamsHttpUtils, ngamsDb, ngamsSubscriber
+from ngamsLib.ngamsCore import getHostName, toiso8601
 from .ngamsTestLib import ngamsTestSuite, tmp_path, genTmpFilename
 
 try:
@@ -437,6 +437,39 @@ def test_subscription_equality(self):
         subs2 = ngamsSubscriber.ngamsSubscriber(url=URL, subscrId='my-id')
         self.assertEqual(subs1, subs2)
 
+        # Store in DB, check equality holds
+        cfg = self.env_aware_cfg()
+        self.point_to_sqlite_database(cfg, tmp_path('ngas.sqlite'))
+        db = ngamsDb.from_config(cfg, maxpool=1)
+        with contextlib.closing(db):
+            db_subs1 = db.insertSubscriberEntry(subs1)
+            db_subs2 = db.insertSubscriberEntry(subs2)
+            self.assertIs(subs1, db_subs1)
+            self.assertEqual(subs1, db_subs2)
+            self.assertEqual(subs2, db_subs2)
+
+    def test_duplicate_subscription(self):
+        """
+        Test that creating multiple subscriptions with the same ID results in
+        different HTTP codes returned to the client
+        """
+        self.prepExtSrv()
+        URL = 'http://127.0.0.1:1234/path'
+        NOW = time.time()
+        START_DATE = toiso8601(NOW, local=True)
+        def subscribe(url=URL, start_date=START_DATE):
+            return self.client.subscribe(url=url, startDate=start_date,
+                                         pars=[['subscr_id', 'my-id']])
+
+        status = subscribe()
+        self.assertEqual(status.http_status, 200)
+        status = subscribe()
+        self.assertEqual(status.http_status, 201)
+        status = subscribe(url=URL + '/subpath')
+        self.assertEqual(status.http_status, 409)
+        status = subscribe(start_date=toiso8601(NOW + 1, local=True))
+        self.assertEqual(status.http_status, 409)
+
     def upload_subscription_files(self, start_port, end_port, pars=[]):
         # Initial archiving
         self.qarchive(start_port, 'src/SmallFile.fits', mimeType='application/octet-stream', pars=pars)