diff --git a/awx/api/serializers.py b/awx/api/serializers.py
index ff3277d18b..a5dee2dc27 100644
--- a/awx/api/serializers.py
+++ b/awx/api/serializers.py
@@ -1640,6 +1640,12 @@ class InventorySourceSerializer(UnifiedJobTemplateSerializer, InventorySourceOpt
     def validate_source_project(self, value):
         if value.scm_type == '':
             raise serializers.ValidationError(_("Can not use manual project for SCM-based inventory."))
+
+    def validate_source(self, value):
+        if value == '':
+            raise serializers.ValidationError(
+                {"source": "Manual inventory sources are created automatically "
+                           "when a group is created in the v1 API."})
         return value
 
     def validate(self, attrs):
diff --git a/awx/main/tests/functional/api/test_inventory.py b/awx/main/tests/functional/api/test_inventory.py
index c74d751ea2..8777b3b384 100644
--- a/awx/main/tests/functional/api/test_inventory.py
+++ b/awx/main/tests/functional/api/test_inventory.py
@@ -342,8 +342,10 @@ class TestControlledBySCM:
 
     def test_adding_inv_src_without_proj_access_prohibited(self, post, project, inventory, rando):
         inventory.admin_role.members.add(rando)
-        post(reverse('api:inventory_inventory_sources_list', kwargs={'pk': inventory.id}),
-             {'name': 'new inv src', 'source_project': project.pk}, rando, expect=403)
+        post(
+            reverse('api:inventory_inventory_sources_list', kwargs={'pk': inventory.id}),
+            {'name': 'new inv src', 'source_project': project.pk, 'source': 'scm', 'overwrite_vars': True},
+            rando, expect=403)
 
     def test_no_post_in_options(self, options, scm_inventory, admin_user):
         r = options(reverse('api:inventory_inventory_sources_list', kwargs={'pk': scm_inventory.id}),