diff --git a/app/lib/activitypub/activity.rb b/app/lib/activitypub/activity.rb
index a6b91f62da..29df445061 100644
--- a/app/lib/activitypub/activity.rb
+++ b/app/lib/activitypub/activity.rb
@@ -176,4 +176,30 @@ class ActivityPub::Activity
     Rails.logger.info("Rejected #{@json['type']} activity #{@json['id']} from #{@account.uri}#{@options[:relayed_through_actor] && "via #{@options[:relayed_through_actor].uri}"}")
     nil
   end
+
+  # Ensure all emojis declared in the activity's tags are
+  # present in the database and downloaded to the local cache.
+  def process_emoji_tags
+    as_array(@object['tag']).each do |tag|
+      process_single_emoji(tag) if tag['type'] == 'Emoji'
+    end
+  end
+
+  def process_single_emoji(tag)
+    parser = ActivityPub::Parser::CustomEmojiParser.new(tag)
+    return if parser.shortcode.blank? || parser.image_remote_url.blank?
+
+    emoji = CustomEmoji.find_by(shortcode: parser.shortcode, domain: @account.domain)
+    return unless emoji.nil? ||
+                  parser.image_remote_url != emoji.image_remote_url ||
+                  (parser.updated_at && parser.updated_at >= emoji.updated_at)
+
+    begin
+      emoji ||= CustomEmoji.new(domain: @account.domain, shortcode: parser.shortcode, uri: parser.uri)
+      emoji.image_remote_url = parser.image_remote_url
+      emoji.save
+    rescue Seahorse::Client::NetworkingError => e
+      Rails.logger.warn "Error fetching emoji: #{e}"
+    end
+  end
 end
diff --git a/app/lib/activitypub/activity/emoji_react.rb b/app/lib/activitypub/activity/emoji_react.rb
index 595751aaae..c3d50b1e05 100644
--- a/app/lib/activitypub/activity/emoji_react.rb
+++ b/app/lib/activitypub/activity/emoji_react.rb
@@ -5,9 +5,16 @@ class ActivityPub::Activity::EmojiReact < ActivityPub::Activity
     original_status = status_from_uri(object_uri)
     name = @json['content']
     return if original_status.nil? ||
-      !original_status.account.local? ||
-      delete_arrived_first?(@json['id']) ||
-      @account.reacted?(original_status, name)
+              !original_status.account.local? ||
+              delete_arrived_first?(@json['id']) ||
+              @account.reacted?(original_status, name)
+
+    if name =~ /^:.*:$/
+      process_emoji_tags
+
+      name.delete! ':'
+      return if CustomEmoji.find_by(shortcode: name, domain: @account.domain).nil?
+    end
 
     reaction = original_status.status_reactions.create!(account: @account, name: name)
 
diff --git a/app/lib/activitypub/activity/like.rb b/app/lib/activitypub/activity/like.rb
index 6af516d109..311a58d3cd 100644
--- a/app/lib/activitypub/activity/like.rb
+++ b/app/lib/activitypub/activity/like.rb
@@ -5,16 +5,7 @@ class ActivityPub::Activity::Like < ActivityPub::Activity
     original_status = status_from_uri(object_uri)
     return if original_status.nil? || !original_status.account.local? || delete_arrived_first?(@json['id'])
 
-    # misskey delivers reactions as likes and attaches the emoji in _misskey_reaction
-    mk_reaction = @json['_misskey_reaction']
-    unless mk_reaction.nil?
-      custom_emoji = CustomEmoji.find_by(shortcode: mk_reaction, domain: @account.domain)
-      return if @account.reacted?(original_status, mk_reaction, custom_emoji)
-
-      reaction = original_status.status_reactions.create!(account: @account, name: mk_reaction, custom_emoji: custom_emoji)
-      LocalNotificationWorker.perform_async(original_status.account_id, reaction.id, 'StatusReaction', 'reaction')
-      return
-    end
+    return if maybe_process_misskey_reaction(original_status)
 
     return if @account.favourited?(original_status)
 
@@ -23,4 +14,25 @@ class ActivityPub::Activity::Like < ActivityPub::Activity
     LocalNotificationWorker.perform_async(original_status.account_id, favourite.id, 'Favourite', 'favourite')
     Trends.statuses.register(original_status)
   end
+
+  # Misskey delivers reactions as likes with the emoji in _misskey_reaction
+  # see https://misskey-hub.net/ns.html#misskey-reaction for details
+  def maybe_process_misskey_reaction(original_status)
+    name = @json['_misskey_reaction']
+    return false if name.nil?
+
+    custom_emoji = nil
+    if name =~ /^:.*:$/
+      process_emoji_tags
+
+      name.delete! ':'
+      custom_emoji = CustomEmoji.find_by(shortcode: name, domain: @account.domain)
+      return false if custom_emoji.nil? # invalid custom emoji, treat it as a regular like
+    end
+    return true if @account.reacted?(original_status, name, custom_emoji)
+
+    reaction = original_status.status_reactions.create!(account: @account, name: name, custom_emoji: custom_emoji)
+    LocalNotificationWorker.perform_async(original_status.account_id, reaction.id, 'StatusReaction', 'reaction')
+    return true
+  end
 end