diff --git a/src/InMemory/InMemoryFile.php b/src/InMemory/InMemoryFile.php
index 5dac723fc..871b67060 100644
--- a/src/InMemory/InMemoryFile.php
+++ b/src/InMemory/InMemoryFile.php
@@ -58,9 +58,7 @@ public function readStream()
 
     public function fileSize(): int
     {
-        return function_exists('mb_strlen')
-            ? mb_strlen($this->contents)
-            : strlen($this->contents);
+        return strlen($this->contents);
     }
 
     public function mimeType(): string