diff --git a/CHANGELOG.md b/CHANGELOG.md
index 530fb40c91..ef33255e91 100755
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@ All notable changes to this project will be documented in this file based on the
 
 ### Bugfixes
 * Always set the Guzzle `base_uri` to support connecting to multiple ES hosts. [#1618](https://github.com/ruflin/Elastica/pull/1618)
+* Properly handle underscore prefixes in bulk request metadata ([cf upstream](https://github.com/elastic/elasticsearch/issues/26886). [#1621](https://github.com/ruflin/Elastica/pull/1621)
 
 ### Added
 
diff --git a/lib/Elastica/Bulk/Action/IndexDocument.php b/lib/Elastica/Bulk/Action/IndexDocument.php
index 1003c1bcef..0899ecf4fe 100644
--- a/lib/Elastica/Bulk/Action/IndexDocument.php
+++ b/lib/Elastica/Bulk/Action/IndexDocument.php
@@ -29,7 +29,9 @@ public function setDocument(Document $document): AbstractDocument
      */
     protected function _getMetadata(AbstractUpdateAction $action): array
     {
-        return $action->getOptions([
+        // see https://github.com/elastic/elasticsearch/issues/26886
+        // for underscore handling
+        $options = $action->getOptions([
             'index',
             'type',
             'id',
@@ -39,5 +41,17 @@ protected function _getMetadata(AbstractUpdateAction $action): array
             'parent',
             'retry_on_conflict',
         ], true);
+
+        $newOptions = \array_intersect_key($options, [
+            '_index' => 1,
+            '_type' => 1,
+            '_id' => 1,
+        ]);
+
+        foreach (\array_diff_key($options, $newOptions) as $k => $v) {
+            $newOptions[\ltrim($k, '_')] = $v;
+        }
+
+        return $newOptions;
     }
 }
diff --git a/test/Elastica/BulkTest.php b/test/Elastica/BulkTest.php
index 2b24642a31..a47118c92c 100644
--- a/test/Elastica/BulkTest.php
+++ b/test/Elastica/BulkTest.php
@@ -639,7 +639,7 @@ public function testRetry()
         $actions = $bulk->getActions();
 
         $metadata = $actions[0]->getMetadata();
-        $this->assertEquals(5, $metadata['_retry_on_conflict']);
+        $this->assertEquals(5, $metadata['retry_on_conflict']);
 
         $script = new Script('');
         $script->setRetryOnConflict(5);
@@ -650,7 +650,7 @@ public function testRetry()
         $actions = $bulk->getActions();
 
         $metadata = $actions[0]->getMetadata();
-        $this->assertEquals(5, $metadata['_retry_on_conflict']);
+        $this->assertEquals(5, $metadata['retry_on_conflict']);
     }
 
     /**