diff --git a/app/models/custom_emoji.rb b/app/models/custom_emoji.rb
index 7e9eb91ca5..58828b0c4c 100644
--- a/app/models/custom_emoji.rb
+++ b/app/models/custom_emoji.rb
@@ -30,9 +30,7 @@ class CustomEmoji < ApplicationRecord
 
   SHORTCODE_RE_FRAGMENT = '[a-zA-Z0-9_]{2,}'
 
-  SCAN_RE = /(?<=[^[:alnum:]:]|\n|^)
-    :(#{SHORTCODE_RE_FRAGMENT}):
-    (?=[^[:alnum:]:]|$)/x
+  SCAN_RE = /:(#{SHORTCODE_RE_FRAGMENT}):/x
   SHORTCODE_ONLY_RE = /\A#{SHORTCODE_RE_FRAGMENT}\z/
 
   IMAGE_MIME_TYPES = %w(image/png image/gif image/webp).freeze