diff --git a/packages/forest_admin_agent/lib/forest_admin_agent/routes/action/actions.rb b/packages/forest_admin_agent/lib/forest_admin_agent/routes/action/actions.rb
index 3a57509b2..6b9689fa7 100644
--- a/packages/forest_admin_agent/lib/forest_admin_agent/routes/action/actions.rb
+++ b/packages/forest_admin_agent/lib/forest_admin_agent/routes/action/actions.rb
@@ -127,6 +127,14 @@ def ensure_served_action(context)
                 "The collection #{context.collection.name} does not have this smart action"
         end
 
+        # A single action runs on its first record, or on nothing: refuse any selection but one id.
+        def ensure_single_record(context, selection_ids)
+          return unless context.collection.schema[:actions][@action_name].scope == Types::ActionScope::SINGLE
+          return unless selection_ids[:are_excluded] || selection_ids[:ids].size != 1
+
+          raise Http::Exceptions::UnprocessableError, 'This action can only be triggered on one record at a time.'
+        end
+
         # Recorded as pending before the action runs and confirmed after, so an action that takes the process
         # down with it still leaves evidence that it started. A failed run is worth recording too — "who tried
         # to run this" is usually the interesting part — and an action answering with an Error result failed
@@ -229,6 +237,7 @@ def get_record_selection(args, context)
           # Restrict the filter to the selected records for single or bulk actions
           if context.collection.schema[:actions][@action_name].scope != Types::ActionScope::GLOBAL
             selection_ids = Utils::Id.parse_selection_ids(context.collection, args[:params])
+            ensure_single_record(context, selection_ids)
             selected_ids = ConditionTreeFactory.match_ids(context.collection, selection_ids[:ids])
             selected_ids = selected_ids.inverse if selection_ids[:are_excluded]
             filter = filter.override(
diff --git a/packages/forest_admin_agent/spec/lib/forest_admin_agent/routes/action/actions_spec.rb b/packages/forest_admin_agent/spec/lib/forest_admin_agent/routes/action/actions_spec.rb
index 2a42a043c..7a0be720a 100644
--- a/packages/forest_admin_agent/spec/lib/forest_admin_agent/routes/action/actions_spec.rb
+++ b/packages/forest_admin_agent/spec/lib/forest_admin_agent/routes/action/actions_spec.rb
@@ -159,6 +159,73 @@ def execute(result: { type: 'Success', message: 'done' }, &raising)
             expect(execute).to eq({ type: 'Success', message: 'done' })
           end
         end
+
+        # A single action context only ever reads the first record, so a selection naming more than one
+        # would run on that record alone and still answer success.
+        describe 'a single action given anything but one record' do
+          let(:action_scope) { ForestAdminDatasourceCustomizer::Decorators::Action::Types::ActionScope::SINGLE }
+          let(:permissions) { instance_spy(ForestAdminAgent::Services::Permissions) }
+          let(:context) do
+            double('context', collection: collection, caller: build_caller, permissions: permissions,
+                              datasource: collection.datasource)
+          end
+          let(:message) { 'This action can only be triggered on one record at a time.' }
+
+          def request(attributes)
+            { params: { data: { attributes: { values: {} }.merge(attributes) } } }
+          end
+
+          before do
+            allow(route).to receive_messages(build: context, build_context_filter: filter)
+            allow(collection).to receive_messages(get_form: [], execute: { type: 'Success', message: 'done' })
+          end
+
+          it 'refuses two ids with a 422 and runs nothing' do
+            expect { route.handle_request(request(ids: %w[4 7])) }
+              .to raise_error(Http::Exceptions::UnprocessableError, message)
+            expect(collection).not_to have_received(:execute)
+          end
+
+          it 'refuses two ids before checking the permissions, so no approval is asked for' do
+            expect { route.handle_request(request(ids: %w[4 7])) }
+              .to raise_error(Http::Exceptions::UnprocessableError, message)
+            expect(permissions).not_to have_received(:can_smart_action?)
+          end
+
+          it 'refuses the approval of a request naming two ids and runs nothing' do
+            signed = JWT.encode({ data: { attributes: { ids: %w[4 7] } } }, Facades::Container.cache(:env_secret), 'HS256')
+
+            expect { route.handle_request(request(ids: %w[4 7], signed_approval_request: signed)) }
+              .to raise_error(Http::Exceptions::UnprocessableError, message)
+            expect(collection).not_to have_received(:execute)
+          end
+
+          it 'refuses an empty selection with a 422 and runs nothing' do
+            expect { route.handle_request(request(ids: [])) }
+              .to raise_error(Http::Exceptions::UnprocessableError, message)
+            expect(collection).not_to have_received(:execute)
+          end
+
+          it 'refuses a select-all selection with a 422 and runs nothing' do
+            expect { route.handle_request(request(ids: [], all_records: true, all_records_ids_excluded: [])) }
+              .to raise_error(Http::Exceptions::UnprocessableError, message)
+            expect(collection).not_to have_received(:execute)
+          end
+
+          it 'refuses loading the form with two ids and computes no form' do
+            expect { route.handle_hook_request(request(ids: %w[4 7])) }
+              .to raise_error(Http::Exceptions::UnprocessableError, message)
+            expect(collection).not_to have_received(:get_form)
+          end
+
+          it 'still runs on exactly one id' do
+            route.handle_request(request(ids: %w[4]))
+
+            expect(collection).to have_received(:execute).with(
+              context.caller, 'Refund', {}, having_attributes(condition_tree: having_attributes(field: 'id', value: 4))
+            )
+          end
+        end
       end
     end
   end