diff -u b/core/modules/views/src/Plugin/views/row/RowPluginBase.php b/core/modules/views/src/Plugin/views/row/RowPluginBase.php
--- b/core/modules/views/src/Plugin/views/row/RowPluginBase.php
+++ b/core/modules/views/src/Plugin/views/row/RowPluginBase.php
@@ -77,7 +77,7 @@
     parent::buildOptionsForm($form, $form_state);
 
     // Warn user if they are setting options for all displays that are not overridden
-    if($this->displayHandler->options['defaults']['style']) {
+    if(isset($this->displayHandler->options['defaults']) && $this->displayHandler->options['defaults']['row']) {
       $form['uses_default_settings'] = array(
         '#prefix' => '<div class="messages messages--warning">',
         '#markup' => $this->t('Changes made here will apply to all displays except overridden. To change Row style options for this display only, you should first override the display Row style.'),
diff -u b/core/modules/views/src/Plugin/views/style/StylePluginBase.php b/core/modules/views/src/Plugin/views/style/StylePluginBase.php
--- b/core/modules/views/src/Plugin/views/style/StylePluginBase.php
+++ b/core/modules/views/src/Plugin/views/style/StylePluginBase.php
@@ -274,7 +274,7 @@
     parent::buildOptionsForm($form, $form_state);
 
     // Warn user if they are setting options for all displays that are not overridden
-    if($this->displayHandler->options['defaults']['style']) {
+    if(isset($this->displayHandler->options['defaults']) && $this->displayHandler->options['defaults']['style']) {
       $form['uses_default_settings'] = array(
         '#prefix' => '<div class="messages messages--warning">',
         '#markup' => $this->t('Changes made here will apply to all displays except overridden. To change style options for this display only, you should first override the display Format.'),