diff --git a/src/wp-includes/meta.php b/src/wp-includes/meta.php
index 19ce664..893cfc5 100644
--- a/src/wp-includes/meta.php
+++ b/src/wp-includes/meta.php
@@ -161,6 +161,7 @@ function update_metadata($meta_type, $object_id, $meta_key, $meta_value, $prev_v
 	$id_column = 'user' == $meta_type ? 'umeta_id' : 'meta_id';
 
 	// expected_slashed ($meta_key)
+	$raw_meta_key = $meta_key;
 	$meta_key = wp_unslash($meta_key);
 	$passed_value = $meta_value;
 	$meta_value = wp_unslash($meta_value);
@@ -198,7 +199,7 @@ function update_metadata($meta_type, $object_id, $meta_key, $meta_value, $prev_v
 
 	$meta_ids = $wpdb->get_col( $wpdb->prepare( "SELECT $id_column FROM $table WHERE meta_key = %s AND $column = %d", $meta_key, $object_id ) );
 	if ( empty( $meta_ids ) ) {
-		return add_metadata($meta_type, $object_id, $meta_key, $passed_value);
+		return add_metadata($meta_type, $object_id, $raw_meta_key, $passed_value);
 	}
 
 	$_meta_value = $meta_value;
diff --git a/tests/phpunit/tests/meta/updateMetadata.php b/tests/phpunit/tests/meta/updateMetadata.php
new file mode 100644
index 0000000..e78d9e1
--- /dev/null
+++ b/tests/phpunit/tests/meta/updateMetadata.php
@@ -0,0 +1,30 @@
+<?php
+
+/**
+ * @group meta
+ * @covers ::update_metadata
+ */
+class Tests_Meta_UpdateMetadata extends WP_UnitTestCase {
+	/**
+	 * @ticket 35795
+	 */
+	public function test_slashed_key_for_new_metadata() {
+		update_metadata( 'post', 123, 'foo\\\\foo', 'bar' );
+
+		$found = get_metadata( 'post', 123, 'foo\foo', true );
+		$this->assertSame( 'bar', $found );
+	}
+
+	/**
+	 * @ticket 35795
+	 */
+	public function test_slashed_key_for_existing_metadata() {
+		global $wpdb;
+
+		add_metadata( 'post', 123, 'foo\\\\foo', 'bar' );
+		update_metadata( 'post', 123, 'foo\\\\foo', 'baz' );
+
+		$found = get_metadata( 'post', 123, 'foo\foo', true );
+		$this->assertSame( 'baz', $found );
+	}
+}