diff --git a/src/wp-admin/includes/schema.php b/src/wp-admin/includes/schema.php
index 911314ea2cbf3..4bfd038eac953 100644
--- a/src/wp-admin/includes/schema.php
+++ b/src/wp-admin/includes/schema.php
@@ -154,7 +154,8 @@ function wp_get_db_schema( $scope = 'all', $blog_id = null ) {
 	meta_value longtext,
 	PRIMARY KEY  (meta_id),
 	KEY post_id (post_id),
-	KEY meta_key (meta_key($max_index_length))
+	KEY meta_key (meta_key($max_index_length)),
+	KEY meta_key_id (meta_key($max_index_length),post_id)
 ) $charset_collate;
 CREATE TABLE $wpdb->posts (
 	ID bigint(20) unsigned NOT NULL auto_increment,
diff --git a/src/wp-admin/includes/upgrade.php b/src/wp-admin/includes/upgrade.php
index 6adb0521ff295..c68fda8e0f54a 100644
--- a/src/wp-admin/includes/upgrade.php
+++ b/src/wp-admin/includes/upgrade.php
@@ -2508,6 +2508,26 @@ function upgrade_700() {
 			)
 		);
 	}
+
+	// Add composite index for meta_key and post_id on postmeta table.
+	if ( $wp_current_db_version < 61697 ) {
+		$max_index_length = 191;
+		// Check if the index already exists.
+		$index_exists = $wpdb->get_var(
+			$wpdb->prepare(
+				"SELECT COUNT(1) FROM INFORMATION_SCHEMA.STATISTICS
+				WHERE table_schema = %s
+				AND table_name = %s
+				AND index_name = 'meta_key_id'",
+				DB_NAME,
+				$wpdb->postmeta
+			)
+		);
+
+		if ( ! $index_exists ) {
+			$wpdb->query( "ALTER TABLE $wpdb->postmeta ADD INDEX meta_key_id (meta_key($max_index_length),post_id)" );
+		}
+	}
 }
 
 /**
diff --git a/src/wp-includes/version.php b/src/wp-includes/version.php
index 9bf095bff6bdb..b560d5ce2e0b6 100644
--- a/src/wp-includes/version.php
+++ b/src/wp-includes/version.php
@@ -23,7 +23,7 @@
  *
  * @global int $wp_db_version
  */
-$wp_db_version = 61696;
+$wp_db_version = 61697;
 
 /**
  * Holds the TinyMCE version.
diff --git a/tests/phpunit/tests/admin/includesSchema.php b/tests/phpunit/tests/admin/includesSchema.php
index 9f2d19f0c16aa..2d32c2058293d 100644
--- a/tests/phpunit/tests/admin/includesSchema.php
+++ b/tests/phpunit/tests/admin/includesSchema.php
@@ -331,4 +331,68 @@ public function data_populate_network_meta() {
 			),
 		);
 	}
+
+	/**
+	 * Test that upgrade_700() adds the composite index to postmeta table.
+	 */
+	public function test_upgrade_700_adds_postmeta_composite_index() {
+		global $wpdb, $wp_current_db_version;
+
+		require_once ABSPATH . 'wp-admin/includes/upgrade.php';
+
+		// Check if index exists first.
+		$index_exists = $wpdb->get_var(
+			$wpdb->prepare(
+				"SELECT COUNT(1) FROM INFORMATION_SCHEMA.STATISTICS
+				WHERE table_schema = %s
+				AND table_name = %s
+				AND index_name = 'meta_key_id'",
+				DB_NAME,
+				$wpdb->postmeta
+			)
+		);
+
+		// Drop the index if it exists to simulate an upgrade scenario.
+		if ( $index_exists > 0 ) {
+			$wpdb->query( "ALTER TABLE $wpdb->postmeta DROP INDEX meta_key_id" );
+		}
+
+		// Verify the index doesn't exist.
+		$index_exists_before = $wpdb->get_var(
+			$wpdb->prepare(
+				"SELECT COUNT(1) FROM INFORMATION_SCHEMA.STATISTICS
+				WHERE table_schema = %s
+				AND table_name = %s
+				AND index_name = 'meta_key_id'",
+				DB_NAME,
+				$wpdb->postmeta
+			)
+		);
+
+		$this->assertSame( 0, (int) $index_exists_before, 'The meta_key_id index should not exist before upgrade.' );
+
+		// Simulate an old database version.
+		$original_db_version   = $wp_current_db_version;
+		$wp_current_db_version = 61696;
+
+		// Run the upgrade function.
+		upgrade_700();
+
+		// Restore original version.
+		$wp_current_db_version = $original_db_version;
+
+		// Verify the index now exists.
+		$index_exists_after = $wpdb->get_var(
+			$wpdb->prepare(
+				"SELECT COUNT(1) FROM INFORMATION_SCHEMA.STATISTICS
+				WHERE table_schema = %s
+				AND table_name = %s
+				AND index_name = 'meta_key_id'",
+				DB_NAME,
+				$wpdb->postmeta
+			)
+		);
+
+		$this->assertGreaterThan( 0, $index_exists_after, 'The meta_key_id composite index should exist after upgrade_700().' );
+	}
 }
diff --git a/tests/phpunit/tests/db/dbDelta.php b/tests/phpunit/tests/db/dbDelta.php
index 23ad16399609e..028d9bb976136 100644
--- a/tests/phpunit/tests/db/dbDelta.php
+++ b/tests/phpunit/tests/db/dbDelta.php
@@ -758,6 +758,32 @@ public function test_wp_get_db_schema_does_not_alter_queries_on_existing_install
 		$this->assertEmpty( $updates );
 	}
 
+	/**
+	 * Test that the postmeta table includes the composite index meta_key_id.
+	 */
+	public function test_postmeta_composite_index_in_schema() {
+		global $wpdb;
+
+		$schema = wp_get_db_schema();
+
+		// Verify that the schema contains the composite index definition.
+		$this->assertStringContainsString( 'KEY meta_key_id', $schema, 'Schema should contain the meta_key_id composite index.' );
+
+		// Verify that the index exists in the actual database.
+		$index_exists = $wpdb->get_var(
+			$wpdb->prepare(
+				"SELECT COUNT(1) FROM INFORMATION_SCHEMA.STATISTICS
+				WHERE table_schema = %s
+				AND table_name = %s
+				AND index_name = 'meta_key_id'",
+				DB_NAME,
+				$wpdb->postmeta
+			)
+		);
+
+		$this->assertGreaterThan( 0, $index_exists, 'The meta_key_id composite index should exist in the postmeta table.' );
+	}
+
 	/**
 	 * @ticket 20263
 	 */