diff --git a/lib/guardian/post_guardian.rb b/lib/guardian/post_guardian.rb
index 791ce8b98f9..ba26c096481 100644
--- a/lib/guardian/post_guardian.rb
+++ b/lib/guardian/post_guardian.rb
@@ -190,8 +190,7 @@ module PostGuardian
     # Can't delete the first post
     return false if post.is_first_post?
 
-    can_moderate = can_moderate_topic?(post.topic)
-    return true if can_moderate
+    return true if can_moderate_topic?(post.topic)
 
     # Can't delete posts in archived topics unless you are staff
     return false if post.topic&.archived?
diff --git a/lib/guardian/topic_guardian.rb b/lib/guardian/topic_guardian.rb
index bf17ca08459..81d36c02c28 100644
--- a/lib/guardian/topic_guardian.rb
+++ b/lib/guardian/topic_guardian.rb
@@ -17,7 +17,7 @@ module TopicGuardian
     return false if anonymous? || topic.nil?
     return true if is_staff?
 
-    is_category_group_moderator?(topic.category)
+    can_perform_action_available_to_group_moderators?(topic)
   end
   alias :can_moderate_topic? :can_review_topic?
 
@@ -132,7 +132,6 @@ module TopicGuardian
       !Post.where(topic_id: topic.id, post_number: 1).where.not(locked_by_id: nil).exists?
   end
 
-  # Recovery Method
   def can_recover_topic?(topic)
     if is_staff? || (topic&.category && is_category_group_moderator?(topic.category))
       !!(topic && topic.deleted_at)
@@ -191,12 +190,9 @@ module TopicGuardian
 
   def filter_allowed_categories(records)
     unless is_admin?
-      allowed_ids = allowed_category_ids
-      if allowed_ids.length > 0
-        records = records.where('topics.category_id IS NULL or topics.category_id IN (?)', allowed_ids)
-      else
-        records = records.where('topics.category_id IS NULL')
-      end
+      records = allowed_category_ids.size == 0 ?
+        records.where('topics.category_id IS NULL') :
+        records.where('topics.category_id IS NULL or topics.category_id IN (?)', allowed_category_ids)
       records = records.references(:categories)
     end
     records
diff --git a/lib/post_merger.rb b/lib/post_merger.rb
index 1cfabc3fbbe..81356f3a500 100644
--- a/lib/post_merger.rb
+++ b/lib/post_merger.rb
@@ -9,12 +9,13 @@ class PostMerger
   end
 
   def merge
-    return unless ensure_at_least_two_posts
+    return if @posts.count < 2
+
     ensure_same_topic!
     ensure_same_user!
 
     guardian = Guardian.new(@user)
-    ensure_staff_user!(guardian)
+    ensure_can_merge!(guardian)
 
     posts = @posts.sort_by do |post|
       guardian.ensure_can_delete!(post)
@@ -38,29 +39,25 @@ class PostMerger
 
   private
 
-  def ensure_at_least_two_posts
-    @posts.count >= 2
-  end
-
   def ensure_same_topic!
-    unless @posts.map(&:topic_id).uniq.length == 1
+    if @posts.map(&:topic_id).uniq.size != 1
       raise CannotMergeError.new(I18n.t("merge_posts.errors.different_topics"))
     end
   end
 
   def ensure_same_user!
-    unless @posts.map(&:user_id).uniq.length == 1
+    if @posts.map(&:user_id).uniq.size != 1
       raise CannotMergeError.new(I18n.t("merge_posts.errors.different_users"))
     end
   end
 
-  def ensure_staff_user!(guardian)
-    raise Discourse::InvalidAccess unless guardian.is_staff?
+  def ensure_can_merge!(guardian)
+    raise Discourse::InvalidAccess unless guardian.can_moderate_topic?(@posts[0].topic)
   end
 
   def ensure_max_post_length!(raw)
     value = StrippedLengthValidator.get_sanitized_value(raw)
-    if value.length > SiteSetting.max_post_length
+    if value.size > SiteSetting.max_post_length
       raise CannotMergeError.new(I18n.t("merge_posts.errors.max_post_length"))
     end
   end
diff --git a/spec/components/post_merger_spec.rb b/spec/components/post_merger_spec.rb
index be1b97a4d1c..e8efd4b19d1 100644
--- a/spec/components/post_merger_spec.rb
+++ b/spec/components/post_merger_spec.rb
@@ -44,11 +44,27 @@ describe PostMerger do
       expect { PostMerger.new(admin, [reply2, post, reply1]).merge }.to raise_error(Discourse::InvalidAccess)
     end
 
-    it "should only allow staff user to merge posts" do
+    it "should only allow staff or TL4 user to merge posts" do
       reply1 = create_post(topic: topic, post_number: post.post_number, user: user)
       reply2 = create_post(topic: topic, post_number: post.post_number, user: user)
 
-      expect { PostMerger.new(user, [reply2, reply1]).merge }.to raise_error(Discourse::InvalidAccess)
+      merged_raw = reply1.raw + "\n\n" + reply2.raw
+
+      tl1 = Fabricate(:user, trust_level: 1)
+      tl2 = Fabricate(:user, trust_level: 2)
+      tl3 = Fabricate(:user, trust_level: 3)
+      tl4 = Fabricate(:user, trust_level: 4)
+
+      expect { PostMerger.new(tl1, [reply2, reply1]).merge }.to raise_error(Discourse::InvalidAccess)
+      expect { PostMerger.new(tl2, [reply2, reply1]).merge }.to raise_error(Discourse::InvalidAccess)
+      expect { PostMerger.new(tl3, [reply2, reply1]).merge }.to raise_error(Discourse::InvalidAccess)
+
+      PostMerger.new(tl4, [reply2, reply1]).merge
+
+      expect(reply1.trashed?).to eq(true)
+      expect(reply2.trashed?).to eq(false)
+
+      expect(reply2.raw).to eq(merged_raw)
     end
 
     it "should not allow posts from different topics to be merged" do