diff --git a/wp-includes/rest-api/class-wp-rest-server.php b/wp-includes/rest-api/class-wp-rest-server.php
index 68be073eef..7f158959e9 100644
--- a/wp-includes/rest-api/class-wp-rest-server.php
+++ b/wp-includes/rest-api/class-wp-rest-server.php
@@ -405,6 +405,11 @@ class WP_REST_Server {
 			 */
 			$result = apply_filters( 'rest_pre_echo_response', $result, $this, $request );
 
+			// The 204 response shouldn't have a body.
+			if ( 204 === $code || null === $result ) {
+				return null;
+			}
+
 			$result = wp_json_encode( $result );
 
 			$json_error_message = $this->get_json_last_error();
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 3d4fc6d0fe..89c22e19d5 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.3-alpha-45808';
+$wp_version = '5.3-alpha-45809';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.