diff --git a/app/BBCode/Tags/Size.php b/app/BBCode/Tags/Size.php
index f3c9094..4f8d53a 100644
--- a/app/BBCode/Tags/Size.php
+++ b/app/BBCode/Tags/Size.php
@@ -57,7 +57,7 @@ class Size extends TagBase
                     if ($size < self::$minSize || $size > self::$maxSize) {
                         return $matches[0];
                     }
-                } elseif (in_array($matches[1], self::$aliases)) {
+                } elseif (array_key_exists($matches[1], self::$aliases)) {
                     $size = self::$aliases[$matches[1]];
                 } else {
                     return $matches[0];