diff --git a/lib/gitlab/github_import/importer/pull_requests_merged_by_importer.rb b/lib/gitlab/github_import/importer/pull_requests_merged_by_importer.rb
index 287e0ea7f7f19e0d31e92e901acd46832a319f73..c56b391cbec7cfa1ecbb90907a37724cb19a8443 100644
--- a/lib/gitlab/github_import/importer/pull_requests_merged_by_importer.rb
+++ b/lib/gitlab/github_import/importer/pull_requests_merged_by_importer.rb
@@ -31,9 +31,7 @@ def id_for_already_imported_cache(merge_request)
         end
 
         def each_object_to_import
-          project.merge_requests.with_state(:merged).find_each do |merge_request|
-            next if already_imported?(merge_request)
-
+          merge_requests_to_import.find_each do |merge_request|
             Gitlab::GithubImport::ObjectCounter.increment(project, object_type, :fetched)
 
             pull_request = client.pull_request(project.import_source, merge_request.iid)
@@ -42,6 +40,17 @@ def each_object_to_import
             mark_as_imported(merge_request)
           end
         end
+
+        private
+
+        # Returns only the merge requests that still have merged_by to be imported.
+        def merge_requests_to_import
+          project.merge_requests.id_not_in(already_imported_objects).with_state(:merged)
+        end
+
+        def already_imported_objects
+          Gitlab::Cache::Import::Caching.values_from_set(already_imported_cache_key)
+        end
       end
     end
   end
diff --git a/lib/gitlab/github_import/importer/pull_requests_reviews_importer.rb b/lib/gitlab/github_import/importer/pull_requests_reviews_importer.rb
index bd65eb5899ce785abfdd697886d07aa3dad64997..5e55d09fe3d6c4068de985ff378fe1fc0ee79aa5 100644
--- a/lib/gitlab/github_import/importer/pull_requests_reviews_importer.rb
+++ b/lib/gitlab/github_import/importer/pull_requests_reviews_importer.rb
@@ -86,7 +86,7 @@ def each_review_page
 
         # Returns only the merge requests that still have reviews to be imported.
         def merge_requests_to_import
-          project.merge_requests.where.not(id: already_imported_merge_requests) # rubocop: disable CodeReuse/ActiveRecord
+          project.merge_requests.id_not_in(already_imported_merge_requests)
         end
 
         def already_imported_merge_requests
diff --git a/spec/lib/gitlab/github_import/importer/pull_requests_merged_by_importer_spec.rb b/spec/lib/gitlab/github_import/importer/pull_requests_merged_by_importer_spec.rb
index 4a47d103cde507970bd72ca57d6b51ee9f49b88d..b6c162aafa962eb379c372a7259bb3772dae5e88 100644
--- a/spec/lib/gitlab/github_import/importer/pull_requests_merged_by_importer_spec.rb
+++ b/spec/lib/gitlab/github_import/importer/pull_requests_merged_by_importer_spec.rb
@@ -4,7 +4,8 @@
 
 RSpec.describe Gitlab::GithubImport::Importer::PullRequestsMergedByImporter do
   let(:client) { double }
-  let(:project) { create(:project, import_source: 'http://somegithub.com') }
+
+  let_it_be(:project) { create(:project, import_source: 'http://somegithub.com') }
 
   subject { described_class.new(project, client) }
 
@@ -27,14 +28,11 @@
   end
 
   describe '#each_object_to_import', :clean_gitlab_redis_cache do
-    it 'fetchs the merged pull requests data' do
-      create(
-        :merged_merge_request,
-        iid: 999,
-        source_project: project,
-        target_project: project
-      )
+    let!(:merge_request) do
+      create(:merged_merge_request, iid: 999, source_project: project, target_project: project)
+    end
 
+    it 'fetches the merged pull requests data' do
       pull_request = double
 
       allow(client)
@@ -48,5 +46,16 @@
 
       subject.each_object_to_import {}
     end
+
+    it 'skips cached merge requests' do
+      Gitlab::Cache::Import::Caching.set_add(
+        "github-importer/already-imported/#{project.id}/pull_requests_merged_by",
+        merge_request.id
+      )
+
+      expect(client).not_to receive(:pull_request)
+
+      subject.each_object_to_import {}
+    end
   end
 end