diff --git a/composer.json b/composer.json
index 8586c5f18..790a1c48e 100644
--- a/composer.json
+++ b/composer.json
@@ -6,6 +6,7 @@
         "respect/validation": "^1.1",
         "smalot/pdfparser": "*",
         "kornrunner/blurhash": "^1.1",
+        "symfony/polyfill-mbstring": "1.20.0",
         "phpcompatibility/php-compatibility": "*"
     },
     "require-dev": {
diff --git a/composer.lock b/composer.lock
index 006645ad0..5dac8f50d 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": "c9a92efe1f2d92a648c4050665f81b05",
+    "content-hash": "9a50d78655731555071e552968158d04",
     "packages": [
         {
             "name": "kornrunner/blurhash",
@@ -290,16 +290,16 @@
         },
         {
             "name": "symfony/polyfill-mbstring",
-            "version": "v1.23.1",
+            "version": "v1.20.0",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/polyfill-mbstring.git",
-                "reference": "9174a3d80210dca8daa7f31fec659150bbeabfc6"
+                "reference": "39d483bdf39be819deabf04ec872eb0b2410b531"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/symfony/polyfill-mbstring/zipball/9174a3d80210dca8daa7f31fec659150bbeabfc6",
-                "reference": "9174a3d80210dca8daa7f31fec659150bbeabfc6",
+                "url": "https://api.github.com/repos/symfony/polyfill-mbstring/zipball/39d483bdf39be819deabf04ec872eb0b2410b531",
+                "reference": "39d483bdf39be819deabf04ec872eb0b2410b531",
                 "shasum": ""
             },
             "require": {
@@ -311,7 +311,7 @@
             "type": "library",
             "extra": {
                 "branch-alias": {
-                    "dev-main": "1.23-dev"
+                    "dev-main": "1.20-dev"
                 },
                 "thanks": {
                     "name": "symfony/polyfill",
@@ -350,7 +350,7 @@
                 "shim"
             ],
             "support": {
-                "source": "https://github.com/symfony/polyfill-mbstring/tree/v1.23.1"
+                "source": "https://github.com/symfony/polyfill-mbstring/tree/v1.20.0"
             },
             "funding": [
                 {
@@ -366,7 +366,7 @@
                     "type": "tidelift"
                 }
             ],
-            "time": "2021-05-27T12:26:48+00:00"
+            "time": "2020-10-23T14:02:19+00:00"
         }
     ],
     "packages-dev": [