diff --git a/assets/js/src/form_editor/store/actions.jsx b/assets/js/src/form_editor/store/actions.jsx
index e07efc9fe8..48d5efbe3b 100644
--- a/assets/js/src/form_editor/store/actions.jsx
+++ b/assets/js/src/form_editor/store/actions.jsx
@@ -75,9 +75,10 @@ export function createCustomFieldDone(response) {
   };
 }
 
-export function createCustomFieldStarted() {
+export function createCustomFieldStarted(customField) {
   return {
     type: 'CREATE_CUSTOM_FIELD_STARTED',
+    customField,
   };
 }
 
diff --git a/assets/js/src/form_editor/store/controls.jsx b/assets/js/src/form_editor/store/controls.jsx
index dc9efa1d75..5b1a1236c9 100644
--- a/assets/js/src/form_editor/store/controls.jsx
+++ b/assets/js/src/form_editor/store/controls.jsx
@@ -68,7 +68,14 @@ export default {
   },
 
   CREATE_CUSTOM_FIELD(action) {
-    dispatch('mailpoet-form-editor').createCustomFieldStarted();
+    if (select('mailpoet-form-editor').getIsCustomFieldCreating()) {
+      return;
+    }
+    dispatch('mailpoet-form-editor').createCustomFieldStarted(action.data);
+    // Check if it really started. Could been blocked by an error.
+    if (!select('mailpoet-form-editor').getIsCustomFieldCreating()) {
+      return;
+    }
     MailPoet.Ajax.post({
       api_version: window.mailpoet_api_version,
       endpoint: 'customFields',
diff --git a/assets/js/src/form_editor/store/reducer.jsx b/assets/js/src/form_editor/store/reducer.jsx
index 46f7b2d0ea..a3380813c9 100644
--- a/assets/js/src/form_editor/store/reducer.jsx
+++ b/assets/js/src/form_editor/store/reducer.jsx
@@ -1,7 +1,7 @@
 import MailPoet from 'mailpoet';
 import createCustomFieldDone from './reducers/create_custom_field_done.jsx';
 import createCustomFieldFailed from './reducers/create_custom_field_failed.jsx';
-import createCustomFieldStarted from './reducers/create_custom_field_started.jsx';
+import createCustomFieldStartedFactory from './reducers/create_custom_field_started.jsx';
 import changeFormName from './reducers/change_form_name.jsx';
 import changeFormSettings from './reducers/change_form_settings.jsx';
 import changeFormStyles from './reducers/change_form_styles.jsx';
@@ -22,6 +22,7 @@ import {
   customFieldDeleteFailed,
 } from './reducers/custom_field_delete.jsx';
 
+const createCustomFieldStarted = createCustomFieldStartedFactory(MailPoet);
 const saveFormStarted = saveFormStartedFactory(MailPoet);
 
 export default (defaultState) => (state = defaultState, action) => {
diff --git a/assets/js/src/form_editor/store/reducers/create_custom_field_started.jsx b/assets/js/src/form_editor/store/reducers/create_custom_field_started.jsx
index 25b7323c3a..b5c25b6cfd 100644
--- a/assets/js/src/form_editor/store/reducers/create_custom_field_started.jsx
+++ b/assets/js/src/form_editor/store/reducers/create_custom_field_started.jsx
@@ -1,8 +1,20 @@
-export default (state) => {
+import { trim } from 'lodash';
+
+export default (MailPoet) => (state, action) => {
   const notices = state.notices.filter((notice) => notice.id !== 'custom-field');
+  const fieldName = trim(action.customField.name);
+  const duplicity = state.customFields.find((field) => (field.name === fieldName));
+  if (duplicity) {
+    notices.push({
+      id: 'custom-field',
+      content: MailPoet.I18n.t('customFieldWithNameExists').replace('[name]', fieldName),
+      isDismissible: true,
+      status: 'error',
+    });
+  }
   return {
     ...state,
-    isCustomFieldCreating: true,
+    isCustomFieldCreating: !duplicity,
     notices,
   };
 };
diff --git a/tests/javascript/form_editor/store/reducers/create_custom_field_started.spec.js b/tests/javascript/form_editor/store/reducers/create_custom_field_started.spec.js
new file mode 100644
index 0000000000..90b9ddc2b3
--- /dev/null
+++ b/tests/javascript/form_editor/store/reducers/create_custom_field_started.spec.js
@@ -0,0 +1,46 @@
+import { expect } from 'chai';
+import reducerFactory from '../../../../../assets/js/src/form_editor/store/reducers/create_custom_field_started.jsx';
+
+const MailPoetStub = {
+  I18n: {
+    t: () => ('Error [name]!'),
+  },
+};
+const reducer = reducerFactory(MailPoetStub);
+
+const dummyCustomField = {
+  name: 'My custom field',
+};
+
+describe('Create Custom Field Started Reducer', () => {
+  let initialState = null;
+  beforeEach(() => {
+    initialState = {
+      notices: [],
+      isCustomFieldCreating: false,
+      customFields: [dummyCustomField],
+    };
+  });
+
+  it('Should set isCustomFieldCreating when there are no errors', () => {
+    const customField = { ...dummyCustomField, name: 'Unique custom field' };
+    const action = {
+      type: 'CREATE_CUSTOM_FIELD_STARTED',
+      customField,
+    };
+    const finalState = reducer(initialState, action);
+    expect(finalState.isCustomFieldCreating).to.equal(true);
+  });
+
+  it('Should create error notice and stop creation process', () => {
+    const customField = { ...dummyCustomField };
+    const action = {
+      type: 'CREATE_CUSTOM_FIELD_STARTED',
+      customField,
+    };
+    const finalState = reducer(initialState, action);
+    expect(finalState.isCustomFieldCreating).to.equal(false);
+    expect(finalState.notices.length).to.equal(1);
+    expect(finalState.notices[0].content).to.equal('Error My custom field!');
+  });
+});
diff --git a/views/form/editor.html b/views/form/editor.html
index 7a61d96239..12e4e976d8 100644
--- a/views/form/editor.html
+++ b/views/form/editor.html
@@ -106,7 +106,8 @@
   'blockAddCustomFieldFormHeading': __('New Custom Field.'),
   'blockCreateButton': _x('Create', 'Label on form submit button.'),
   'customFieldName': _x('Field name', 'Label for form field for custom input name'),
-  'selectCustomFieldType': _x('Select a field type', 'Label for form field for custom input type')
+  'selectCustomFieldType': _x('Select a field type', 'Label for form field for custom input type'),
+  'customFieldWithNameExists': __('The custom field [name] already exists. Please choose another name.')
 }) %>
 <% endblock %>