diff --git a/app/controllers/posts_controller.rb b/app/controllers/posts_controller.rb
index 2a905751ab7..520aab3bccd 100644
--- a/app/controllers/posts_controller.rb
+++ b/app/controllers/posts_controller.rb
@@ -321,14 +321,12 @@ class PostsController < ApplicationController
 
   def destroy
     post = find_post_from_params
+    force_destroy = ActiveModel::Type::Boolean.new.cast(params[:force_destroy])
 
-    force_destroy = false
-    if params[:force_destroy].present?
+    if force_destroy
       if !guardian.can_permanently_delete?(post)
         return render_json_error post.cannot_permanently_delete_reason(current_user), status: 403
       end
-
-      force_destroy = true
     else
       guardian.ensure_can_delete!(post)
     end
@@ -338,8 +336,12 @@ class PostsController < ApplicationController
       RateLimiter.new(current_user, "delete_post_per_day", SiteSetting.max_post_deletions_per_day, 1.day).performed!
     end
 
-    destroyer = PostDestroyer.new(current_user, post, context: params[:context], force_destroy: force_destroy)
-    destroyer.destroy
+    PostDestroyer.new(
+      current_user,
+      post,
+      context: params[:context],
+      force_destroy: force_destroy
+    ).destroy
 
     render body: nil
   end
diff --git a/app/controllers/topics_controller.rb b/app/controllers/topics_controller.rb
index 909f540af1f..be5f02f41ac 100644
--- a/app/controllers/topics_controller.rb
+++ b/app/controllers/topics_controller.rb
@@ -621,20 +621,22 @@ class TopicsController < ApplicationController
 
   def destroy
     topic = Topic.with_deleted.find_by(id: params[:id])
+    force_destroy = ActiveModel::Type::Boolean.new.cast(params[:force_destroy])
 
-    force_destroy = false
-    if params[:force_destroy].present?
+    if force_destroy
       if !guardian.can_permanently_delete?(topic)
         return render_json_error topic.cannot_permanently_delete_reason(current_user), status: 403
       end
-
-      force_destroy = true
     else
       guardian.ensure_can_delete!(topic)
     end
 
-    first_post = topic.posts.with_deleted.order(:post_number).first
-    PostDestroyer.new(current_user, first_post, context: params[:context], force_destroy: force_destroy).destroy
+    PostDestroyer.new(
+      current_user,
+      topic.ordered_posts.with_deleted.first,
+      context: params[:context],
+      force_destroy: force_destroy
+    ).destroy
 
     render body: nil
   rescue Discourse::InvalidAccess
diff --git a/app/models/topic.rb b/app/models/topic.rb
index 9b2dff1e98a..54af4242de7 100644
--- a/app/models/topic.rb
+++ b/app/models/topic.rb
@@ -1786,7 +1786,12 @@ class Topic < ActiveRecord::Base
   end
 
   def cannot_permanently_delete_reason(user)
-    if self.posts_count > 0
+    all_posts_count = Post.with_deleted
+      .where(topic_id: self.id)
+      .where(post_type: [Post.types[:regular], Post.types[:moderator_action], Post.types[:whisper]])
+      .count
+
+    if posts_count > 0 || all_posts_count > 1
       I18n.t('post.cannot_permanently_delete.many_posts')
     elsif self.deleted_by_id == user&.id && self.deleted_at >= Post::PERMANENT_DELETE_TIMER.ago
       time_left = RateLimiter.time_left(Post::PERMANENT_DELETE_TIMER.to_i - Time.zone.now.to_i + self.deleted_at.to_i)
diff --git a/lib/guardian/topic_guardian.rb b/lib/guardian/topic_guardian.rb
index f5cff4eefc8..06141292247 100644
--- a/lib/guardian/topic_guardian.rb
+++ b/lib/guardian/topic_guardian.rb
@@ -158,7 +158,20 @@ module TopicGuardian
   def can_permanently_delete_topic?(topic)
     return false if !SiteSetting.can_permanently_delete
     return false if !topic
+
+    # Ensure that all posts (including small actions) are at least soft
+    # deleted.
     return false if topic.posts_count > 0
+
+    # All other posts that were deleted still must be permanently deleted
+    # before the topic can be deleted with the exception of small action
+    # posts that will be deleted right before the topic is.
+    all_posts_count = Post.with_deleted
+      .where(topic_id: topic.id)
+      .where(post_type: [Post.types[:regular], Post.types[:moderator_action], Post.types[:whisper]])
+      .count
+    return false if all_posts_count > 1
+
     return false if !is_admin? || !can_see_topic?(topic)
     return false if !topic.deleted_at
     return false if topic.deleted_by_id == @user.id && topic.deleted_at >= Post::PERMANENT_DELETE_TIMER.ago
diff --git a/lib/post_destroyer.rb b/lib/post_destroyer.rb
index 57d9bb3d011..cd0f037b168 100644
--- a/lib/post_destroyer.rb
+++ b/lib/post_destroyer.rb
@@ -145,6 +145,14 @@ class PostDestroyer
   # show up in the topic
   # Permanent option allows to hard delete.
   def perform_delete
+    # All posts in the topic must be force deleted if the first is force
+    # deleted (except @post which is destroyed by current instance).
+    if @topic && @post.is_first_post? && permanent?
+      @topic.ordered_posts.with_deleted.reverse_order.find_each do |post|
+        PostDestroyer.new(@user, post, @opts).destroy if post.id != @post.id
+      end
+    end
+
     Post.transaction do
       permanent? ? @post.destroy! : @post.trash!(@user)
       if @post.topic
diff --git a/spec/models/topic_spec.rb b/spec/models/topic_spec.rb
index b21761e952e..54a6bd0e0ed 100644
--- a/spec/models/topic_spec.rb
+++ b/spec/models/topic_spec.rb
@@ -3030,6 +3030,9 @@ RSpec.describe Topic do
       expect(topic.reload.cannot_permanently_delete_reason(Fabricate(:admin))).to eq(I18n.t('post.cannot_permanently_delete.many_posts'))
 
       PostDestroyer.new(admin, post_2.reload).destroy
+      expect(topic.reload.cannot_permanently_delete_reason(Fabricate(:admin))).to eq(I18n.t('post.cannot_permanently_delete.many_posts'))
+
+      PostDestroyer.new(admin, post_2.reload, force_destroy: true).destroy
       expect(topic.reload.cannot_permanently_delete_reason(Fabricate(:admin))).to eq(nil)
     end
 
diff --git a/spec/requests/topics_controller_spec.rb b/spec/requests/topics_controller_spec.rb
index b67f235d8b6..0ed754a064a 100644
--- a/spec/requests/topics_controller_spec.rb
+++ b/spec/requests/topics_controller_spec.rb
@@ -1188,6 +1188,48 @@ RSpec.describe TopicsController do
         end
       end
     end
+
+    describe 'force destroy' do
+      fab!(:post) { Fabricate(:post, topic: topic, post_number: 1) }
+
+      before do
+        SiteSetting.can_permanently_delete = true
+
+        sign_in(admin)
+      end
+
+      it 'force destroys all deleted small actions in topic too' do
+        small_action_post = Fabricate(:small_action, topic: topic)
+        PostDestroyer.new(Discourse.system_user, post).destroy
+        PostDestroyer.new(Discourse.system_user, small_action_post).destroy
+
+        delete "/t/#{topic.id}.json", params: { force_destroy: true }
+
+        expect(response.status).to eq(200)
+
+        expect(Topic.find_by(id: topic.id)).to eq(nil)
+        expect(Post.find_by(id: post.id)).to eq(nil)
+        expect(Post.find_by(id: small_action_post.id)).to eq(nil)
+      end
+
+      it 'does not allow to destroy topic if not all posts were force destroyed' do
+        other_post = Fabricate(:post, topic: topic, post_number: 2)
+        PostDestroyer.new(Discourse.system_user, post).destroy
+
+        delete "/t/#{topic.id}.json", params: { force_destroy: true }
+
+        expect(response.status).to eq(403)
+      end
+
+      it 'does not allow to destroy topic if not all small action posts were deleted' do
+        small_action_post = Fabricate(:small_action, topic: topic)
+        PostDestroyer.new(Discourse.system_user, small_action_post).destroy
+
+        delete "/t/#{topic.id}.json", params: { force_destroy: true }
+
+        expect(response.status).to eq(403)
+      end
+    end
   end
 
   describe '#id_for_slug' do