diff --git a/drfpasswordless/serializers.py b/drfpasswordless/serializers.py
index af40098..94b4fe3 100644
--- a/drfpasswordless/serializers.py
+++ b/drfpasswordless/serializers.py
@@ -85,7 +85,7 @@ class MobileAuthSerializer(AbstractBaseAliasAuthenticationSerializer):
     def alias_type(self):
         return 'mobile'
 
-    phone_regex = RegexValidator(regex=r'^\+?[1-9]\d{1,14}$',
+    phone_regex = RegexValidator(regex=r'^\+[1-9]\d{1,14}$',
                                  message="Mobile number must be entered in the format:"
                                          " '+999999999'. Up to 15 digits allowed.")
     mobile = serializers.CharField(validators=[phone_regex], max_length=17)
@@ -169,7 +169,7 @@ class AbstractBaseCallbackTokenSerializer(serializers.Serializer):
     Abstract class inspired by DRF's own token serializer.
     Returns a user if valid, None or a message if not.
     """
-    phone_regex = RegexValidator(regex=r'^\+?[1-9]\d{1,14}$',
+    phone_regex = RegexValidator(regex=r'^\+[1-9]\d{1,14}$',
                                  message="Mobile number must be entered in the format:"
                                          " '+999999999'. Up to 15 digits allowed.")
 
diff --git a/tests/models.py b/tests/models.py
index 935d88c..8bf3795 100644
--- a/tests/models.py
+++ b/tests/models.py
@@ -3,7 +3,7 @@
 from django.core.validators import RegexValidator
 from django.db import models
 
-phone_regex = RegexValidator(regex=r'^\+?[1-9]\d{1,14}$',
+phone_regex = RegexValidator(regex=r'^\+[1-9]\d{1,14}$',
                              message="Mobile number must be entered in the format:"
                                      " '+999999999'. Up to 15 digits allowed.")