diff --git a/changelogs/unreleased/sh-enforce-unique-and-not-null-project-ids-project-features.yml b/changelogs/unreleased/sh-enforce-unique-and-not-null-project-ids-project-features.yml
new file mode 100644
index 0000000000000000000000000000000000000000..aae42b66c845203fe5a11310944745c8bd7edea0
--- /dev/null
+++ b/changelogs/unreleased/sh-enforce-unique-and-not-null-project-ids-project-features.yml
@@ -0,0 +1,5 @@
+---
+title: Add a unique and not null constraint on the project_features.project_id column
+merge_request:
+author:
+type: fixed
diff --git a/db/post_migrate/20180511174224_add_unique_constraint_to_project_features_project_id.rb b/db/post_migrate/20180511174224_add_unique_constraint_to_project_features_project_id.rb
new file mode 100644
index 0000000000000000000000000000000000000000..88a9f5f825662698114ba08d7d7b4e13398e7d36
--- /dev/null
+++ b/db/post_migrate/20180511174224_add_unique_constraint_to_project_features_project_id.rb
@@ -0,0 +1,43 @@
+class AddUniqueConstraintToProjectFeaturesProjectId < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  class ProjectFeature < ActiveRecord::Base
+    self.table_name = 'project_features'
+
+    include EachBatch
+  end
+
+  def up
+    remove_duplicates
+
+    add_concurrent_index :project_features, :project_id, unique: true, name: 'index_project_features_on_project_id_unique'
+    remove_concurrent_index_by_name :project_features, 'index_project_features_on_project_id'
+    rename_index :project_features, 'index_project_features_on_project_id_unique', 'index_project_features_on_project_id'
+  end
+
+  def down
+    rename_index :project_features, 'index_project_features_on_project_id', 'index_project_features_on_project_id_old'
+    add_concurrent_index :project_features, :project_id
+    remove_concurrent_index_by_name :project_features, 'index_project_features_on_project_id_old'
+  end
+
+  private
+
+  def remove_duplicates
+    features = ProjectFeature
+               .select('MAX(id) AS max, COUNT(id), project_id')
+               .group(:project_id)
+               .having('COUNT(id) > 1')
+
+    features.each do |feature|
+      ProjectFeature
+        .where(project_id: feature['project_id'])
+        .where('id <> ?', feature['max'])
+        .each_batch { |batch| batch.delete_all }
+    end
+  end
+end
diff --git a/db/post_migrate/20180512061621_add_not_null_constraint_to_project_features_project_id.rb b/db/post_migrate/20180512061621_add_not_null_constraint_to_project_features_project_id.rb
new file mode 100644
index 0000000000000000000000000000000000000000..5a6d6ff4a1091e5743c376030c837329a86dbbe4
--- /dev/null
+++ b/db/post_migrate/20180512061621_add_not_null_constraint_to_project_features_project_id.rb
@@ -0,0 +1,21 @@
+class AddNotNullConstraintToProjectFeaturesProjectId < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  class ProjectFeature < ActiveRecord::Base
+    include EachBatch
+
+    self.table_name = 'project_features'
+  end
+
+  def up
+    ProjectFeature.where(project_id: nil).delete_all
+
+    change_column_null :project_features, :project_id, false
+  end
+
+  def down
+    change_column_null :project_features, :project_id, true
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 4abca1789a09b57cb958b09c3553409f26dd9a9f..ed29d202f914a37fcbba12c379ec98f142aafe5e 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20180511090724) do
+ActiveRecord::Schema.define(version: 20180512061621) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -1494,7 +1494,7 @@ ActiveRecord::Schema.define(version: 20180511090724) do
   add_index "project_deploy_tokens", ["project_id", "deploy_token_id"], name: "index_project_deploy_tokens_on_project_id_and_deploy_token_id", unique: true, using: :btree
 
   create_table "project_features", force: :cascade do |t|
-    t.integer "project_id"
+    t.integer "project_id", null: false
     t.integer "merge_requests_access_level"
     t.integer "issues_access_level"
     t.integer "wiki_access_level"
@@ -1505,7 +1505,7 @@ ActiveRecord::Schema.define(version: 20180511090724) do
     t.integer "repository_access_level", default: 20, null: false
   end
 
-  add_index "project_features", ["project_id"], name: "index_project_features_on_project_id", using: :btree
+  add_index "project_features", ["project_id"], name: "index_project_features_on_project_id", unique: true, using: :btree
 
   create_table "project_group_links", force: :cascade do |t|
     t.integer "project_id", null: false
diff --git a/lib/gitlab/import_export/relation_factory.rb b/lib/gitlab/import_export/relation_factory.rb
index e3e9f156fb43a4c12cb6a13089b5d46e897fdbb9..4a41a69840b54fc1ad8e752365705c1ca53e4fd2 100644
--- a/lib/gitlab/import_export/relation_factory.rb
+++ b/lib/gitlab/import_export/relation_factory.rb
@@ -28,7 +28,7 @@ module Gitlab
 
       IMPORTED_OBJECT_MAX_RETRIES = 5.freeze
 
-      EXISTING_OBJECT_CHECK = %i[milestone milestones label labels project_label project_labels group_label group_labels].freeze
+      EXISTING_OBJECT_CHECK = %i[milestone milestones label labels project_label project_labels group_label group_labels project_feature].freeze
 
       TOKEN_RESET_MODELS = %w[Ci::Trigger Ci::Build ProjectHook].freeze
 
diff --git a/spec/migrations/add_unique_constraint_to_project_features_project_id_spec.rb b/spec/migrations/add_unique_constraint_to_project_features_project_id_spec.rb
new file mode 100644
index 0000000000000000000000000000000000000000..bf299b70a29686459fca4e7218b24678b6df2afc
--- /dev/null
+++ b/spec/migrations/add_unique_constraint_to_project_features_project_id_spec.rb
@@ -0,0 +1,59 @@
+require 'spec_helper'
+require Rails.root.join('db', 'post_migrate', '20180511174224_add_unique_constraint_to_project_features_project_id.rb')
+
+describe AddUniqueConstraintToProjectFeaturesProjectId, :migration do
+  let(:namespaces) { table(:namespaces) }
+  let(:projects) { table(:projects) }
+  let(:features) { table(:project_features) }
+  let(:migration) { described_class.new }
+
+  describe '#up' do
+    before do
+      (1..3).each do |i|
+        namespaces.create(id: i, name: "ns-test-#{i}", path: "ns-test-i#{i}")
+        projects.create!(id: i, name: "test-#{i}", path: "test-#{i}", namespace_id: i)
+      end
+
+      features.create!(id: 1, project_id: 1)
+      features.create!(id: 2, project_id: 1)
+      features.create!(id: 3, project_id: 2)
+      features.create!(id: 4, project_id: 2)
+      features.create!(id: 5, project_id: 2)
+      features.create!(id: 6, project_id: 3)
+    end
+
+    it 'creates a unique index and removes duplicates' do
+      expect(migration.index_exists?(:project_features, :project_id, unique: false, name: 'index_project_features_on_project_id')).to be true
+
+      expect { migration.up }.to change { features.count }.from(6).to(3)
+
+      expect(migration.index_exists?(:project_features, :project_id, unique: true, name: 'index_project_features_on_project_id')).to be true
+      expect(migration.index_exists?(:project_features, :project_id, name: 'index_project_features_on_project_id_unique')).to be false
+
+      project_1_features = features.where(project_id: 1)
+      expect(project_1_features.count).to eq(1)
+      expect(project_1_features.first.id).to eq(2)
+
+      project_2_features = features.where(project_id: 2)
+      expect(project_2_features.count).to eq(1)
+      expect(project_2_features.first.id).to eq(5)
+
+      project_3_features = features.where(project_id: 3)
+      expect(project_3_features.count).to eq(1)
+      expect(project_3_features.first.id).to eq(6)
+    end
+  end
+
+  describe '#down' do
+    it 'restores the original index' do
+      migration.up
+
+      expect(migration.index_exists?(:project_features, :project_id, unique: true, name: 'index_project_features_on_project_id')).to be true
+
+      migration.down
+
+      expect(migration.index_exists?(:project_features, :project_id, unique: false, name: 'index_project_features_on_project_id')).to be true
+      expect(migration.index_exists?(:project_features, :project_id, name: 'index_project_features_on_project_id_old')).to be false
+    end
+  end
+end
diff --git a/spec/models/guest_spec.rb b/spec/models/guest_spec.rb
index 2afdd6751a476053586d7339d4b7ac059e45a342..fc30f3056e50112cd7ba4f540f527cc88fdc90f9 100644
--- a/spec/models/guest_spec.rb
+++ b/spec/models/guest_spec.rb
@@ -1,9 +1,9 @@
 require 'spec_helper'
 
 describe Guest do
-  let(:public_project) { build_stubbed(:project, :public) }
-  let(:private_project) { build_stubbed(:project, :private) }
-  let(:internal_project) { build_stubbed(:project, :internal) }
+  set(:public_project) { create(:project, :public) }
+  set(:private_project) { create(:project, :private) }
+  set(:internal_project) { create(:project, :internal) }
 
   describe '.can_pull?' do
     context 'when project is private' do