diff --git a/core/lib/Drupal/Core/Config/Entity/Query/Query.php b/core/lib/Drupal/Core/Config/Entity/Query/Query.php
index 81c3dfb..40144ed 100644
--- a/core/lib/Drupal/Core/Config/Entity/Query/Query.php
+++ b/core/lib/Drupal/Core/Config/Entity/Query/Query.php
@@ -128,31 +128,37 @@ protected function loadRecords() {
     $prefix = $entity_info->getConfigPrefix() . '.';
     $prefix_length = strlen($prefix);
 
-    // If there are conditions on the config ID, we can narrow the list of
-    // records to load and parse.
+    // Search the conditions for restrictions on entity IDs.
     $ids = array();
     if ($this->condition->getConjunction() == 'AND') {
       foreach ($this->condition->conditions() as $condition) {
-        if ($condition['field'] == $entity_info->getKey('id')) {
+        if (is_string($condition['field']) && $condition['field'] == $entity_info->getKey('id')) {
           $operator = $condition['operator'] ?: (is_array($condition['value']) ? 'IN' : '=');
-          if ($operator == '=' || $operator == 'IN') {
-            $ids = is_array($condition['value']) ? $condition['value'] : array($condition['value']);
-            // We can stop at the first condition on ID. In the (weird) case
-            // where other conditions additionally restrict IDs, results will
-            // be eliminated when the conditions are checked on the loaded
-            // records.
+          if ($operator == '=') {
+            $ids = array($condition['value']);
+          }
+          elseif ($operator == 'IN') {
+            $ids = $condition['value'];
+          }
+          // We stop at the first restricting condition on ID. In the (weird)
+          // case where there are additional restricting conditions, results
+          // will be eliminated when the conditions are checked on the loaded
+          // records.
+          if ($ids) {
             break;
           }
         }
       }
     }
+    // If there are conditions restricting config ID, we can narrow the list of
+    // records to load and parse.
     if ($ids) {
       $names = array_map(function ($id) use ($prefix) {
         return $prefix . $id;
       }, $ids);
     }
+    // If no restrictions on IDs were found, we need to parse all records.
     else {
-      // If no conditions on IDs were found, we need to parse all records.
       $names = $this->configStorage->listAll($prefix);
     }