diff --git a/app/models/project_statistics.rb b/app/models/project_statistics.rb
index 832c8417b5b..dd0654aec0b 100644
--- a/app/models/project_statistics.rb
+++ b/app/models/project_statistics.rb
@@ -48,7 +48,7 @@ class ProjectStatistics < ApplicationRecord
 
   # older migrations fail due to non-existent attribute without this
   def packages_size
-    has_attribute?(:packages_size) ? super.to_i : 0
+    has_attribute?(:packages_size) ? super : 0
   end
 
   def update_storage_size
diff --git a/changelogs/unreleased/ac-namespaces-stats-no-coalesce.yml b/changelogs/unreleased/ac-namespaces-stats-no-coalesce.yml
new file mode 100644
index 00000000000..bd005206d4e
--- /dev/null
+++ b/changelogs/unreleased/ac-namespaces-stats-no-coalesce.yml
@@ -0,0 +1,5 @@
+---
+title: Forbid NULL in project_statistics.packages_size
+merge_request: 28400
+author:
+type: other
diff --git a/db/migrate/20190516155724_change_packages_size_defaults_in_project_statistics.rb b/db/migrate/20190516155724_change_packages_size_defaults_in_project_statistics.rb
new file mode 100644
index 00000000000..eba154df496
--- /dev/null
+++ b/db/migrate/20190516155724_change_packages_size_defaults_in_project_statistics.rb
@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+class ChangePackagesSizeDefaultsInProjectStatistics < ActiveRecord::Migration[5.1]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    change_column_default :project_statistics, :packages_size, 0
+
+    update_column_in_batches(:project_statistics, :packages_size, 0) do |table, query|
+      query.where(table[:packages_size].eq(nil))
+    end
+
+    change_column_null :project_statistics, :packages_size, false
+  end
+
+  def down
+    change_column_null :project_statistics, :packages_size, true
+    change_column_default :project_statistics, :packages_size, nil
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 89140048ad3..1fdfb73eb59 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -1744,7 +1744,7 @@ ActiveRecord::Schema.define(version: 20190527194900) do
     t.bigint "repository_size", default: 0, null: false
     t.bigint "lfs_objects_size", default: 0, null: false
     t.bigint "build_artifacts_size", default: 0, null: false
-    t.bigint "packages_size"
+    t.bigint "packages_size", default: 0, null: false
     t.bigint "wiki_size"
     t.index ["namespace_id"], name: "index_project_statistics_on_namespace_id", using: :btree
     t.index ["project_id"], name: "index_project_statistics_on_project_id", unique: true, using: :btree
diff --git a/spec/migrations/change_packages_size_defaults_in_project_statistics_spec.rb b/spec/migrations/change_packages_size_defaults_in_project_statistics_spec.rb
new file mode 100644
index 00000000000..93e7e9304b1
--- /dev/null
+++ b/spec/migrations/change_packages_size_defaults_in_project_statistics_spec.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('db', 'migrate', '20190516155724_change_packages_size_defaults_in_project_statistics.rb')
+
+describe ChangePackagesSizeDefaultsInProjectStatistics, :migration do
+  let(:project_statistics) { table(:project_statistics) }
+  let(:projects)           { table(:projects) }
+
+  it 'removes null packages_size' do
+    stats_to_migrate = 10
+
+    stats_to_migrate.times do |i|
+      p = projects.create!(name: "project #{i}", namespace_id: 1)
+      project_statistics.create!(project_id: p.id, namespace_id: p.namespace_id)
+    end
+
+    expect { migrate! }
+      .to change { ProjectStatistics.where(packages_size: nil).count }
+            .from(stats_to_migrate)
+            .to(0)
+  end
+
+  it 'defaults packages_size to 0' do
+    project = projects.create!(name: 'a new project', namespace_id: 2)
+    stat = project_statistics.create!(project_id: project.id, namespace_id: project.namespace_id)
+
+    expect(stat.packages_size).to be_nil
+
+    migrate!
+
+    stat.reload
+    expect(stat.packages_size).to eq(0)
+  end
+end