diff -u b/src/Plugin/Field/FieldWidget/ParagraphsWidget.php b/src/Plugin/Field/FieldWidget/ParagraphsWidget.php
--- b/src/Plugin/Field/FieldWidget/ParagraphsWidget.php
+++ b/src/Plugin/Field/FieldWidget/ParagraphsWidget.php
@@ -670,10 +670,10 @@
             $subform_state = SubformState::createForSubform($element['behavior_plugins'][$plugin_id], $form, $form_state);
             if ($plugin_form = $plugin->buildBehaviorForm($paragraphs_entity, $element['behavior_plugins'][$plugin_id], $subform_state)) {
               $element['behavior_plugins'][$plugin_id] = $plugin_form;
+              // Add the paragraphs-behavior class, so that we are able to show
+              // and hide behavior fields, depending on the active perspective.
+              $element['behavior_plugins'][$plugin_id]['#attributes']['class'][] = 'paragraphs-behavior';
             }
-            // Add the paragraphs-behavior class, so that we are able to show
-            // and hide behavior fields, depending on the active perspective.
-            $element['behavior_plugins'][$plugin_id]['#attributes']['class'][] = 'paragraphs-behavior';
           }
         }
       }