diff --git a/core/lib/Drupal/Core/Database/Driver/mysql/Schema.php b/core/lib/Drupal/Core/Database/Driver/mysql/Schema.php
index 81b56a2..fcbb717 100644
--- a/core/lib/Drupal/Core/Database/Driver/mysql/Schema.php
+++ b/core/lib/Drupal/Core/Database/Driver/mysql/Schema.php
@@ -267,7 +267,16 @@ protected function createKeysSql($spec) {
     }
     if (!empty($spec['indexes'])) {
       foreach ($spec['indexes'] as $index => $fields) {
-        $keys[] = 'INDEX `' . $index . '` (' . $this->createKeySql($fields) . ')';
+        $duplicateIndex = true;
+        foreach ($fields as $i => $field) {
+          if ($spec['primary key'][$i] != $field) {
+            $duplicateIndex = false;
+            break;
+          }
+        }
+        if ($duplicateIndex === false) {
+          $keys[] = 'INDEX `' . $index . '` (' . $this->createKeySql($fields) . ')';
+        }
       }
     }