diff -u b/src/Form/SensorForm.php b/src/Form/SensorForm.php
--- b/src/Form/SensorForm.php
+++ b/src/Form/SensorForm.php
@@ -238,8 +238,7 @@
     }
 
     if ($default_config = $plugin->getDefaultConfiguration()) {
-      $form_state->setValue(['settings', 'table'], $default_config['table']);
-      $form_state->setValue(['settings', 'aggregation', 'time_interval_field'], $default_config['time_interval_field']);
+      $form_state->setValue('settings', $default_config);
     }
 
     $plugin->validateConfigurationForm($form, $form_state);
diff -u b/src/Plugin/monitoring/SensorPlugin/WatchdogAggregatorSensorPlugin.php b/src/Plugin/monitoring/SensorPlugin/WatchdogAggregatorSensorPlugin.php
--- b/src/Plugin/monitoring/SensorPlugin/WatchdogAggregatorSensorPlugin.php
+++ b/src/Plugin/monitoring/SensorPlugin/WatchdogAggregatorSensorPlugin.php
@@ -54,10 +54,12 @@
    * {@inheritdoc}
    */
   public function getDefaultConfiguration() {
-    $default_config = [
+    $default_config = array(
       'table' => 'watchdog',
-      'time_interval_field' => 'timestamp',
-     ];
+      'aggregation' => array(
+        'time_interval_field' => 'timestamp',
+      ),
+    );
     return $default_config;
   }
 
diff -u b/src/Tests/MonitoringUITest.php b/src/Tests/MonitoringUITest.php
--- b/src/Tests/MonitoringUITest.php
+++ b/src/Tests/MonitoringUITest.php
@@ -177,7 +177,7 @@
     $sensor_theme = SensorConfig::load('core_theme_default');
     $this->assertTrue($sensor_theme->status());
 
-    // Test the creation of a Watchdog sensor.
+    // Test the creation of a Watchdog sensor with default configuration.
     $this->drupalGet('admin/config/system/monitoring/sensors/add');
     $this->drupalPostForm(NULL, array(
       'label' => 'Watchdog Sensor',