diff --git a/src/wp-includes/rest-api/fields/class-wp-rest-meta-fields.php b/src/wp-includes/rest-api/fields/class-wp-rest-meta-fields.php
index e0b4144..b332255 100644
--- a/src/wp-includes/rest-api/fields/class-wp-rest-meta-fields.php
+++ b/src/wp-includes/rest-api/fields/class-wp-rest-meta-fields.php
@@ -311,7 +311,7 @@ abstract class WP_REST_Meta_Fields {
 		$old_value = get_metadata( $meta_type, $object_id, $meta_key );
 
 		if ( 1 === count( $old_value ) ) {
-			if ( $old_value[0] === $meta_value ) {
+			if ( $old_value[0] === sanitize_meta( $meta_key, $meta_value, $meta_type ) ) {
 				return true;
 			}
 		}
diff --git a/tests/phpunit/tests/rest-api/rest-post-meta-fields.php b/tests/phpunit/tests/rest-api/rest-post-meta-fields.php
index dc7c72e..92cd225 100644
--- a/tests/phpunit/tests/rest-api/rest-post-meta-fields.php
+++ b/tests/phpunit/tests/rest-api/rest-post-meta-fields.php
@@ -120,6 +120,13 @@ class WP_Test_REST_Post_Meta_Fields extends WP_Test_REST_TestCase {
 			)
 		);
 
+		register_meta( 'post', 'test_sanitized', array(
+			'single'            => true,
+			'show_in_rest'      => true,
+			'type'              => 'string',
+			'sanitize_callback' => array( $this, 'set_duplicate_single_value_after_sanitization_sanitize_callback' ),
+		) );
+
 		/** @var WP_REST_Server $wp_rest_server */
 		global $wp_rest_server;
 		$this->server = $wp_rest_server = new Spy_REST_Server;
@@ -355,6 +362,39 @@ class WP_Test_REST_Post_Meta_Fields extends WP_Test_REST_TestCase {
 		$this->assertEquals( 'test_value', $meta['test_single'] );
 	}
 
+	public function test_set_duplicate_single_value_after_sanitization() {
+
+		$value     = 'abc5def';
+		$sanitized = 'abcdef';
+		update_post_meta( self::$post_id, 'test_sanitized', $value );
+
+		$this->grant_write_permission();
+
+		$data    = array(
+			'meta' => array(
+				'test_sanitized' => $value,
+			),
+		);
+		$request = new WP_REST_Request( 'POST', sprintf( '/wp/v2/posts/%d', self::$post_id ) );
+		$request->set_body_params( $data );
+
+		$response = $this->server->dispatch( $request );
+		$this->assertEquals( 200, $response->get_status() );
+
+		$meta = get_post_meta( self::$post_id, 'test_sanitized', true );
+		$this->assertNotEmpty( $meta );
+		$this->assertEquals( $sanitized, $meta );
+
+		$data = $response->get_data();
+		$meta = (array) $data['meta'];
+		$this->assertArrayHasKey( 'test_sanitized', $meta );
+		$this->assertEquals( $sanitized, $meta['test_sanitized'] );
+	}
+
+	public function set_duplicate_single_value_after_sanitization_sanitize_callback( $value ) {
+		return preg_replace( '/[^a-z]/', '', $value );
+	}
+
 	/**
 	 * @depends test_set_value
 	 */