diff --git a/app/controllers/admin/editions_controller.rb b/app/controllers/admin/editions_controller.rb
index df07efe1c66..4bdda6bfdfc 100644
--- a/app/controllers/admin/editions_controller.rb
+++ b/app/controllers/admin/editions_controller.rb
@@ -401,14 +401,32 @@ def set_default_edition_locations
     end
   end
 
+  # TODO: not sure this is the way forward. We can't reset orgs to [] because some update calls will
+  # naturally omit orgs, and we get a whole bunch of failing tests.
+  # I'm also not convinced we should set supporting orgs to [] if lead_orgs association is present.
+  # Feels a bit unclean - if we wanted to configure 'supporting orgs only' then that should perhaps
+  # be possible.
+  # Instead it feels like we should have some mechanism for saying:
+  # - Here's the current edition
+  # - Here's what the edition will be if the save completes
+  # - Has the current user lost access in this transition? If so, raise validation error
   def delete_absent_edition_organisations
     return if edition_params.empty?
 
-    if edition_params[:lead_organisation_ids]
-      edition_params[:lead_organisation_ids] = edition_params[:lead_organisation_ids].reject(&:blank?)
+    if @edition.respond_to?(:lead_organisation_ids)
+      edition_params[:lead_organisation_ids] = if edition_params[:lead_organisation_ids].blank?
+                                                 []
+                                               else
+                                                 edition_params[:lead_organisation_ids].reject(&:blank?)
+                                               end
     end
-    if edition_params[:supporting_organisation_ids]
-      edition_params[:supporting_organisation_ids] = edition_params[:supporting_organisation_ids].reject(&:blank?)
+
+    if @edition.respond_to?(:supporting_organisation_ids)
+      edition_params[:supporting_organisation_ids] = if edition_params[:supporting_organisation_ids].blank?
+                                                       []
+                                                     else
+                                                       edition_params[:supporting_organisation_ids].reject(&:blank?)
+                                                     end
     end
   end
 
diff --git a/test/functional/admin/standard_editions_controller_test.rb b/test/functional/admin/standard_editions_controller_test.rb
index 02547e0a472..f4f6648c80c 100644
--- a/test/functional/admin/standard_editions_controller_test.rb
+++ b/test/functional/admin/standard_editions_controller_test.rb
@@ -1181,6 +1181,45 @@ class Admin::StandardEditionsControllerTest < ActionController::TestCase
     assert_select "textarea[name='edition[block_content][sidebar]']", text: "My sidebar content"
   end
 
+  test "treats absence of supporting_organisation_ids as an empty array" do
+    login_as create(:user, organisation: nil)
+
+    configurable_document_type = build_configurable_document_type(
+      "test_type",
+      {
+        "forms" => {
+          "documents" => {
+            "fields" => {
+              "supporting_organisations" => {
+                "title" => "Supporting organisations",
+                "block" => "select_with_search_tagging",
+                "container" => "organisations",
+                "attribute_path" => %w[supporting_organisation_ids],
+                "translatable" => false,
+              },
+            },
+          },
+        },
+      },
+    )
+    ConfigurableDocumentType.setup_test_types(configurable_document_type)
+
+    edition = create(:standard_edition, configurable_document_type: "test_type", supporting_organisation_ids: [create(:organisation).id])
+    assert_not edition.supporting_organisation_ids.empty?
+
+    patch :update, params: {
+      id: edition,
+      edition: {
+        # minimal permitted attrs to avoid strong params rejection
+        title: edition.title,
+        summary: edition.summary,
+      },
+      save: "save",
+    }
+    assert_response :redirect
+    assert edition.reload.supporting_organisation_ids.empty?
+  end
+
   view_test "GET edit renders hidden current_tab field for the default tab when document type defines tabs" do
     configurable_document_type = build_configurable_document_type("test_type", {
       "forms" => {