diff --git a/app/models/custom_emoji.rb b/app/models/custom_emoji.rb
index 2f78aab91be044..8a640bbb1b7d94 100644
--- a/app/models/custom_emoji.rb
+++ b/app/models/custom_emoji.rb
@@ -27,9 +27,9 @@ class CustomEmoji < ApplicationRecord
 
   SHORTCODE_RE_FRAGMENT = '[a-zA-Z0-9_]{2,}'
 
-  SCAN_RE = /(?<=[^[:alnum:]:]|\n|^)
+  SCAN_RE = /(?<=[^a-zA-Z0-9]|\n|^)
     :(#{SHORTCODE_RE_FRAGMENT}):
-    (?=[^[:alnum:]:]|$)/x
+    (?=[^a-zA-Z0-9]|$)/x
   SHORTCODE_ONLY_RE = /\A#{SHORTCODE_RE_FRAGMENT}\z/
 
   IMAGE_MIME_TYPES = %w(image/jpeg image/png image/gif image/webp).freeze