diff --git a/src/Plugin/Field/FieldWidget/InlineEntityFormComplex.php b/src/Plugin/Field/FieldWidget/InlineEntityFormComplex.php
index 0859058..f52d21d 100644
--- a/src/Plugin/Field/FieldWidget/InlineEntityFormComplex.php
+++ b/src/Plugin/Field/FieldWidget/InlineEntityFormComplex.php
@@ -3,6 +3,8 @@
 namespace Drupal\inline_entity_form\Plugin\Field\FieldWidget;
 
 use Drupal\Component\Utility\NestedArray;
+use Drupal\Component\Utility\Tags;
+use Drupal\Core\Entity\Element\EntityAutocomplete;
 use Drupal\Core\Entity\EntityDisplayRepositoryInterface;
 use Drupal\Core\Entity\EntityTypeBundleInfoInterface;
 use Drupal\Core\Entity\EntityTypeManagerInterface;
@@ -566,12 +568,69 @@ class InlineEntityFormComplex extends InlineEntityFormBase implements ContainerF
     // If the inline entity form is still open, then its entity hasn't
     // been transferred to the IEF form state yet.
     if (empty($values) && !empty($widget_state['form'])) {
-      // @todo Do the same for reference forms.
       if ($widget_state['form'] == 'add') {
         $element = NestedArray::getValue($form, [$field_name, 'widget', 'form']);
         $entity = $element['inline_entity_form']['#entity'];
         $values[] = ['entity' => $entity];
       }
+      else if ($widget_state['form'] == 'ief_add_existing') {
+        $element = NestedArray::getValue($form, [$field_name, 'widget', 'form'])['entity_id'];
+        if (!empty($element['#value'])) {
+          $options = array(
+            'target_type' => $element['#target_type'],
+            'handler' => $element['#selection_handler'],
+            'handler_settings' => $element['#selection_settings'],
+          );
+          /** @var /Drupal\Core\Entity\EntityReferenceSelection\SelectionInterface $handler */
+          $handler = \Drupal::service('plugin.manager.entity_reference_selection')
+            ->getInstance($options);
+          $input_values = $element['#tags'] ? Tags::explode($element['#value']) : array($element['#value']);
+
+          foreach ($input_values as $input) {
+            $match = EntityAutocomplete::extractEntityIdFromAutocompleteInput($input);
+            if ($match === NULL) {
+              // Try to get a match from the input string when the user didn't use
+              // the autocomplete but filled in a value manually.
+              $entities_by_bundle = $handler->getReferenceableEntities($input, '=');
+              $entities = array_reduce($entities_by_bundle, function ($flattened, $bundle_entities) {
+                return $flattened + $bundle_entities;
+              }, []);
+              $params = array(
+                '%value' => $input,
+                '@value' => $input,
+              );
+              if (empty($entities)) {
+                $form_state->setError($element, t('There are no entities matching "%value".', $params));
+              }
+              elseif (count($entities) > 5) {
+                $params['@id'] = key($entities);
+                // Error if there are more than 5 matching entities.
+                $form_state->setError($element, t('Many entities are called %value. Specify the one you want by appending the id in parentheses, like "@value (@id)".', $params));
+              }
+              elseif (count($entities) > 1) {
+                // More helpful error if there are only a few matching entities.
+                $multiples = array();
+                foreach ($entities as $id => $name) {
+                  $multiples[] = $name . ' (' . $id . ')';
+                }
+                $params['@id'] = $id;
+                $form_state->setError($element, t('Multiple entities match this reference; "%multiple". Specify the one you want by appending the id in parentheses, like "@value (@id)".', array('%multiple' => implode('", "', $multiples)) + $params));
+              }
+              else {
+                // Take the one and only matching entity.
+                $values += array(
+                  'target_id' => key($entities),
+                );
+              }
+            }
+            else {
+              $values += array(
+                'target_id' => $match,
+              );
+            }
+          }
+        }
+      }
     }
     // Sort values by weight.
     uasort($values, '\Drupal\Component\Utility\SortArray::sortByWeightElement');
diff --git a/src/Tests/ComplexWidgetWebTest.php b/src/Tests/ComplexWidgetWebTest.php
index 974c8a0..121024f 100644
--- a/src/Tests/ComplexWidgetWebTest.php
+++ b/src/Tests/ComplexWidgetWebTest.php
@@ -432,6 +432,42 @@ class ComplexWidgetWebTest extends InlineEntityFormTestBase {
   }
 
   /**
+   * Tests if referencing an existing entity works without submitting the form.
+   */
+  public function testReferencingExistingEntitiesNoSubmit() {
+    // Allow addition of existing nodes.
+    $this->setAllowExisting(TRUE);
+    $title = $this->randomMachineName();
+
+    $this->drupalCreateNode([
+      'type' => 'ief_reference_type',
+      'title' => $title,
+      'first_name' => $this->randomMachineName(),
+      'last_name' => $this->randomMachineName(),
+    ]);
+    $node = $this->drupalGetNodeByTitle($title);
+    $this->assertTrue($node, 'Created ief_reference_type node "' . $node->label() . '"');;
+
+    $this->drupalGet($this->formContentAddUrl);
+    $this->drupalPostAjaxForm(NULL, [], $this->getButtonName('//input[@type="submit" and @value="Add existing node" and @data-drupal-selector="edit-multi-actions-ief-add-existing"]'));
+    $this->assertResponse(200, 'Opening inline form for existing entity was successful.');
+
+    $parent_title = $this->randomMachineName();
+    $edit = [
+      'multi[form][entity_id]' => $node->getTitle() . ' (' . $node->id() . ')',
+      'title[0][value]' => $parent_title,
+    ];
+
+    // Create ief_test_complex node.
+    $this->assertFieldByName('multi[form][entity_id]', NULL, 'Existing entity reference autocomplete field found.');
+    $this->drupalPostForm(NULL, $edit, t('Save'));
+    $this->assertResponse(200, 'Submission of parent entity was successful.');
+    $this->assertNoText(t("This value should not be null."), "The error message 'This value cannot be null' was not found in the page.");
+    $node = $this->drupalGetNodeByTitle($parent_title);
+    $this->assertTrue($node, 'Created ief_reference_type node.');
+  }
+
+  /**
    * Test if invalid values get correct validation messages in reference existing entity form.
    *
    * Also checks if existing entity reference form can be canceled.