diff --git a/src/wp-includes/rest-api/endpoints/class-wp-rest-users-controller.php b/src/wp-includes/rest-api/endpoints/class-wp-rest-users-controller.php
index e3e5d935d7a1a..34edf2c6e63d0 100644
--- a/src/wp-includes/rest-api/endpoints/class-wp-rest-users-controller.php
+++ b/src/wp-includes/rest-api/endpoints/class-wp-rest-users-controller.php
@@ -719,7 +719,7 @@ public function update_item( $request ) {
 			);
 		}
 
-		$owner_id = email_exists( $request['email'] );
+		$owner_id = ! empty( $request['email'] ) && is_string( $request['email'] ) ? email_exists( $request['email'] ) : false;
 
 		if ( $owner_id && $owner_id !== $id ) {
 			return new WP_Error(