diff --git a/composer.json b/composer.json
index 39afe3536..b8d0c9fe5 100644
--- a/composer.json
+++ b/composer.json
@@ -52,6 +52,7 @@
         "phpmd/phpmd": "^2.6",
         "phan/phan": "^4.0",
         "phpunit/phpunit": "^7.5",
-        "skaut/phan-wordpress-stubs": "^1.0.0"
+        "skaut/phan-wordpress-stubs": "^1.0.0",
+        "symfony/polyfill-mbstring": "^1.20.0 <1.22"
     }
 }
diff --git a/composer.lock b/composer.lock
index cb98d80ae..32ed2f1de 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "8fda6822d805fe77b7d87a5379a7710a",
+    "content-hash": "e910be70c65eb50902f5c7eb4cebd987",
     "packages": [
         {
             "name": "firebase/php-jwt",
@@ -3909,16 +3909,16 @@
         },
         {
             "name": "symfony/polyfill-mbstring",
-            "version": "v1.22.0",
+            "version": "v1.20.0",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/polyfill-mbstring.git",
-                "reference": "f377a3dd1fde44d37b9831d68dc8dea3ffd28e13"
+                "reference": "39d483bdf39be819deabf04ec872eb0b2410b531"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/symfony/polyfill-mbstring/zipball/f377a3dd1fde44d37b9831d68dc8dea3ffd28e13",
-                "reference": "f377a3dd1fde44d37b9831d68dc8dea3ffd28e13",
+                "url": "https://api.github.com/repos/symfony/polyfill-mbstring/zipball/39d483bdf39be819deabf04ec872eb0b2410b531",
+                "reference": "39d483bdf39be819deabf04ec872eb0b2410b531",
                 "shasum": ""
             },
             "require": {
@@ -3930,7 +3930,7 @@
             "type": "library",
             "extra": {
                 "branch-alias": {
-                    "dev-main": "1.22-dev"
+                    "dev-main": "1.20-dev"
                 },
                 "thanks": {
                     "name": "symfony/polyfill",
@@ -3982,7 +3982,7 @@
                     "type": "tidelift"
                 }
             ],
-            "time": "2021-01-07T16:49:33+00:00"
+            "time": "2020-10-23T14:02:19+00:00"
         },
         {
             "name": "symfony/polyfill-php73",
diff --git a/gulpfile.js b/gulpfile.js
index ed0f33d72..cfeb96642 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -284,7 +284,6 @@ gulp.task( 'build:deps:composer:other', function () {
 				'vendor/symfony/polyfill-intl-idn/bootstrap.php',
 				'vendor/symfony/polyfill-intl-idn/Idn.php',
 				'vendor/symfony/polyfill-mbstring/bootstrap.php',
-				'vendor/symfony/polyfill-mbstring/bootstrap80.php',
 				'vendor/symfony/polyfill-mbstring/Mbstring.php',
 			],
 			{ base: 'vendor/' }
diff --git a/src/php/class-api-facade.php b/src/php/class-api-facade.php
index af43523e1..e40aafb77 100644
--- a/src/php/class-api-facade.php
+++ b/src/php/class-api-facade.php
@@ -236,7 +236,7 @@ private static function list_files( $parent_id, $fields, $order_by, $pagination_
 			throw new \Sgdg\Exceptions\Unsupported_Value_Exception( $fields, 'list_files' );
 		}
 		if ( $fields->check( array( 'id', 'name' ) ) ) {
-			$mime_type_check = '(mimeType contains "' . $mime_type_prefix . '" or (mimeType = "application/vnd.google-apps.shortcut" and shortcutDetails.targetMimeType contains "' . $mime_type_prefix . '"))';
+			$mime_type_check = '(mimeType contains "' . $mime_type_prefix . '" or (mimeType contains "application/vnd.google-apps.shortcut" and shortcutDetails.targetMimeType contains "' . $mime_type_prefix . '"))';
 		} else {
 			$mime_type_check = 'mimeType contains "' . $mime_type_prefix . '"';
 		}