diff --git a/app/lib/activitypub/activity/emoji_react.rb b/app/lib/activitypub/activity/emoji_react.rb
index c9d88bc51c..ad9f9abbaa 100644
--- a/app/lib/activitypub/activity/emoji_react.rb
+++ b/app/lib/activitypub/activity/emoji_react.rb
@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 class ActivityPub::Activity::EmojiReact < ActivityPub::Activity
+  CUSTOM_EMOJI_REGEX = /^:[^:]+:$/
+
   def perform
     original_status = status_from_uri(object_uri)
     name = @json['content']
@@ -8,7 +10,7 @@ class ActivityPub::Activity::EmojiReact < ActivityPub::Activity
               !original_status.account.local? ||
               delete_arrived_first?(@json['id'])
 
-    if /^:.*:$/.match?(name)
+    if CUSTOM_EMOJI_REGEX.match?(name)
       name.delete! ':'
       custom_emoji = process_emoji_tags(name, @json['tag'])
 
diff --git a/app/lib/activitypub/activity/like.rb b/app/lib/activitypub/activity/like.rb
index 0063820825..8856f7be4c 100644
--- a/app/lib/activitypub/activity/like.rb
+++ b/app/lib/activitypub/activity/like.rb
@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 class ActivityPub::Activity::Like < ActivityPub::Activity
+  CUSTOM_EMOJI_REGEX = /^:[^:]+:$/
+
   def perform
     original_status = status_from_uri(object_uri)
     return if original_status.nil? || !original_status.account.local? || delete_arrived_first?(@json['id'])
@@ -23,7 +25,7 @@ class ActivityPub::Activity::Like < ActivityPub::Activity
     name = @json['content'] || @json['_misskey_reaction']
     return false if name.nil?
 
-    if /^:.*:$/.match?(name)
+    if CUSTOM_EMOJI_REGEX.match?(name)
       name.delete! ':'
       custom_emoji = process_emoji_tags(name, @json['tag'])
 
diff --git a/app/lib/activitypub/activity/undo.rb b/app/lib/activitypub/activity/undo.rb
index 5f9f1bbecb..0c7714d6ed 100644
--- a/app/lib/activitypub/activity/undo.rb
+++ b/app/lib/activitypub/activity/undo.rb
@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 class ActivityPub::Activity::Undo < ActivityPub::Activity
+  CUSTOM_EMOJI_REGEX = /^:[^:]+:$/
+
   def perform
     case @object['type']
     when 'Announce'
@@ -125,7 +127,7 @@ class ActivityPub::Activity::Undo < ActivityPub::Activity
 
     return if status.nil? || !status.account.local?
 
-    if /^:.*:$/.match?(name)
+    if CUSTOM_EMOJI_REGEX.match?(name)
       name.delete! ':'
       custom_emoji = process_emoji_tags(name, @object['tag'])