diff --git a/apps/account/models.py b/apps/account/models.py
index b0ae79d6..508a52fd 100644
--- a/apps/account/models.py
+++ b/apps/account/models.py
@@ -52,10 +52,6 @@ class UserQuerySet(models.QuerySet):
         return self.filter(oauth2_provider_refreshtoken__token=token,
                            oauth2_provider_refreshtoken__expires__gt=timezone.now())
 
-    def by_username(self, username: str):
-        """Filter users by username."""
-        return self.filter(username=username)
-
 
 class User(ImageMixin, AbstractUser):
     """Base user model."""
diff --git a/apps/account/serializers/common.py b/apps/account/serializers/common.py
index 2f88d426..deb0217e 100644
--- a/apps/account/serializers/common.py
+++ b/apps/account/serializers/common.py
@@ -43,11 +43,13 @@ class UserSerializer(serializers.ModelSerializer):
         """Validate email value"""
         if value == self.instance.email:
             raise serializers.ValidationError()
+        if models.User.objects.filter(email=value).exists():
+            raise serializers.ValidationError()
         return value
 
     def validate_username(self, value):
         """Validate username"""
-        if models.User.objects.by_username(username=value).exists():
+        if models.User.objects.filter(username=value).exists():
             raise serializers.ValidationError()
         return value