diff --git a/app/models/account.rb b/app/models/account.rb
index 31a5deadc82..e5737909452 100644
--- a/app/models/account.rb
+++ b/app/models/account.rb
@@ -122,6 +122,7 @@ class Account < ApplicationRecord
 
   # Remote user validations
   validates :uri, presence: true, exclusion: { in: [''] }, uniqueness: true, unless: :local?, on: :create
+  validates :inbox_url, presence: true, if: -> { !local? && (new_record? || will_save_change_to_inbox_url?) }
 
   # Local user validations
   validates :username, format: { with: /\A[a-z0-9_]+\z/i }, length: { maximum: USERNAME_LENGTH_LIMIT }, if: -> { local? && will_save_change_to_username? && !actor_type_application? }
diff --git a/spec/fabricators/account_fabricator.rb b/spec/fabricators/account_fabricator.rb
index 6a5218cee98..7e1e1b4349e 100644
--- a/spec/fabricators/account_fabricator.rb
+++ b/spec/fabricators/account_fabricator.rb
@@ -12,6 +12,7 @@ Fabricator(:account) do
   silenced_at           { |attrs| attrs[:silenced] ? Time.now.utc : nil }
   requested_deletion_at { |attrs| attrs[:requested_deletion] ? Time.now.utc : nil }
   user                  { |attrs| attrs[:domain].nil? ? Fabricate.build(:user, account: nil) : nil }
+  inbox_url             { |attrs| attrs[:domain].nil? ? '' : "https://#{attrs[:domain]}/users/#{attrs[:username]}/inbox" }
   uri                   { |attrs| attrs[:domain].nil? ? nil : "https://#{attrs[:domain]}/users/#{attrs[:username]}" }
   discoverable          true
   indexable             true
diff --git a/spec/models/account_spec.rb b/spec/models/account_spec.rb
index 70d349d13ad..a1735af6c37 100644
--- a/spec/models/account_spec.rb
+++ b/spec/models/account_spec.rb
@@ -745,12 +745,12 @@ RSpec.describe Account do
   context 'when is remote' do
     it 'does not generate keys' do
       key = OpenSSL::PKey::RSA.new(1024).public_key
-      account = described_class.create!(domain: 'remote', uri: 'https://remote/actor', username: 'remote_user_with_public', public_key: key.to_pem)
+      account = described_class.create!(domain: 'remote', uri: 'https://remote/actor', inbox_url: 'https://remote/actor/inbox', username: 'remote_user_with_public', public_key: key.to_pem)
       expect(account.keypair.keypair.params).to eq key.params
     end
 
     it 'normalizes domain' do
-      account = described_class.create!(domain: 'にゃん', uri: 'https://xn--r9j5b5b/actor', username: 'remote_user_with_idn_domain')
+      account = described_class.create!(domain: 'にゃん', uri: 'https://xn--r9j5b5b/actor', inbox_url: 'https://xn--r9j5b5b/actor/inbox', username: 'remote_user_with_idn_domain')
       expect(account.domain).to eq 'xn--r9j5b5b'
     end
   end