diff -u b/core/modules/text/src/Plugin/Field/FieldWidget/TextareaWidget.php b/core/modules/text/src/Plugin/Field/FieldWidget/TextareaWidget.php
--- b/core/modules/text/src/Plugin/Field/FieldWidget/TextareaWidget.php
+++ b/core/modules/text/src/Plugin/Field/FieldWidget/TextareaWidget.php
@@ -36,9 +36,11 @@
     $element['#format'] = $items[$delta]->format;
     $element['#base_type'] = $main_widget['value']['#type'];
 
-    $allowed_formats = array_filter($this->getFieldSetting('allowed_formats'));
-    if (!empty($allowed_formats) && !$this->isDefaultValueWidget($form_state)) {
-      $element['#allowed_formats'] = $allowed_formats;
+    if (is_array($this->getFieldSetting('allowed_formats'))) {
+      $allowed_formats = array_filter($this->getFieldSetting('allowed_formats'));
+      if (!empty($allowed_formats) && !$this->isDefaultValueWidget($form_state)) {
+        $element['#allowed_formats'] = $allowed_formats;
+      }
     }
 
     return $element;
diff -u b/core/modules/text/src/Plugin/Field/FieldWidget/TextfieldWidget.php b/core/modules/text/src/Plugin/Field/FieldWidget/TextfieldWidget.php
--- b/core/modules/text/src/Plugin/Field/FieldWidget/TextfieldWidget.php
+++ b/core/modules/text/src/Plugin/Field/FieldWidget/TextfieldWidget.php
@@ -36,9 +36,11 @@
     $element['#format'] = isset($items[$delta]->format) ? $items[$delta]->format : NULL;
     $element['#base_type'] = $main_widget['value']['#type'];
 
-    $allowed_formats = array_filter($this->getFieldSetting('allowed_formats'));
-    if (!empty($allowed_formats) && !$this->isDefaultValueWidget($form_state)) {
-      $element['#allowed_formats'] = $allowed_formats;
+    if (is_array($this->getFieldSetting('allowed_formats'))) {
+      $allowed_formats = array_filter($this->getFieldSetting('allowed_formats'));
+      if (!empty($allowed_formats) && !$this->isDefaultValueWidget($form_state)) {
+        $element['#allowed_formats'] = $allowed_formats;
+      }
     }
 
     return $element;