diff --git a/README.md b/README.md
index 2203a2c..6fe49a7 100644
--- a/README.md
+++ b/README.md
@@ -320,6 +320,9 @@ DEFAULTS = {
     # configurable function for sending sms
     'PASSWORDLESS_SMS_CALLBACK': 'drfpasswordless.utils.send_sms_with_callback_token'
 
+    # Token Generation Retry Count
+    'PASSWORDLESS_TOKEN_GENERATION_ATTEMPTS': 3
+
 
 }
 ```
diff --git a/drfpasswordless/__init__.py b/drfpasswordless/__init__.py
index 6f0ab97..e9802b2 100644
--- a/drfpasswordless/__init__.py
+++ b/drfpasswordless/__init__.py
@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 
 __title__ = 'drfpasswordless'
-__version__ = '1.5.6'
+__version__ = '1.5.7'
 __author__ = 'Aaron Ng'
 __license__ = 'MIT'
 __copyright__ = 'Copyright 2020 Aaron Ng'
diff --git a/drfpasswordless/__version__.py b/drfpasswordless/__version__.py
index 6897abd..e3cced8 100644
--- a/drfpasswordless/__version__.py
+++ b/drfpasswordless/__version__.py
@@ -1,3 +1,3 @@
-VERSION = (1, 5, 6)
+VERSION = (1, 5, 7)
 
 __version__ = '.'.join(map(str, VERSION))
diff --git a/drfpasswordless/migrations/0005_auto_20201117_0410.py b/drfpasswordless/migrations/0005_auto_20201117_0410.py
new file mode 100644
index 0000000..7057588
--- /dev/null
+++ b/drfpasswordless/migrations/0005_auto_20201117_0410.py
@@ -0,0 +1,17 @@
+# Generated by Django 3.0.2 on 2020-11-17 04:10
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('drfpasswordless', '0004_auto_20200125_0853'),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name='callbacktoken',
+            unique_together=set(),
+        ),
+    ]
diff --git a/drfpasswordless/models.py b/drfpasswordless/models.py
index fd3557e..d09f3fc 100644
--- a/drfpasswordless/models.py
+++ b/drfpasswordless/models.py
@@ -47,7 +47,6 @@ class Meta:
         abstract = True
         get_latest_by = 'created_at'
         ordering = ['-id']
-        unique_together = (('key', 'is_active'),)
 
     def __str__(self):
         return str(self.key)
@@ -66,4 +65,3 @@ class CallbackToken(AbstractBaseCallbackToken):
 
     class Meta(AbstractBaseCallbackToken.Meta):
         verbose_name = 'Callback Token'
-        unique_together = ['is_active', 'key', 'type']
diff --git a/drfpasswordless/settings.py b/drfpasswordless/settings.py
index f7f6e0b..5b93197 100644
--- a/drfpasswordless/settings.py
+++ b/drfpasswordless/settings.py
@@ -88,6 +88,8 @@
     'PASSWORDLESS_EMAIL_CALLBACK': 'drfpasswordless.utils.send_email_with_callback_token',
     'PASSWORDLESS_SMS_CALLBACK': 'drfpasswordless.utils.send_sms_with_callback_token',
 
+    # Token Generation Retry Count
+    'PASSWORDLESS_TOKEN_GENERATION_ATTEMPTS': 3
 }
 
 # List of settings that may be in string import notation.
diff --git a/drfpasswordless/signals.py b/drfpasswordless/signals.py
index ac5e063..33adf6d 100644
--- a/drfpasswordless/signals.py
+++ b/drfpasswordless/signals.py
@@ -1,5 +1,6 @@
 import logging
 from django.contrib.auth import get_user_model
+from django.core.exceptions import ValidationError
 from django.dispatch import receiver
 from django.db.models import signals
 from drfpasswordless.models import CallbackToken
@@ -27,18 +28,41 @@ def invalidate_previous_tokens(sender, instance, created, **kwargs):
 def check_unique_tokens(sender, instance, **kwargs):
     """
     Ensures that mobile and email tokens are unique or tries once more to generate.
+    Note that here we've decided keys are unique even across auth and validation.
+    We could consider relaxing this in the future as well by filtering on the instance.type.
     """
     if instance._state.adding:
         # save is called on a token to create it in the db
         # before creating check whether a token with the same key exists
         if isinstance(instance, CallbackToken):
+            unique = False
+            tries = 0
+                
             if CallbackToken.objects.filter(key=instance.key, is_active=True).exists():
-                instance.key = generate_numeric_token()
+                # Try N(default=3) times before giving up.
+                while tries < api_settings.PASSWORDLESS_TOKEN_GENERATION_ATTEMPTS:
+                    tries = tries + 1
+                    new_key = generate_numeric_token()
+                    instance.key = new_key
+                
+                    if not CallbackToken.objects.filter(key=instance.key, is_active=True).exists():
+                        # Leave the loop if we found a valid token that doesn't exist yet.
+                        unique = True
+                        break
+
+                if not unique:
+                    # A unique value wasn't found after three tries
+                    raise ValidationError("Couldn't create a unique token even after retrying.")
+            else:
+                # A unique value was found immediately.
+                pass
+
+        
     else:
         # save is called on an already existing token to update it. Such as invalidating it.
         # in that case there is no need to check for the key. This way we both avoid an unneccessary db hit
         # and avoid to change key field of used tokens.
-        pass 
+        pass