diff --git a/deploy/invoice_number_counter.sql b/deploy/invoice_number_counter.sql
index 2713e6b..07330ad 100644
--- a/deploy/invoice_number_counter.sql
+++ b/deploy/invoice_number_counter.sql
@@ -7,7 +7,7 @@ begin;
 set search_path to numerus, public;
 
 create table invoice_number_counter (
-	company_id integer not null,
+	company_id integer not null references company,
 	year integer not null constraint year_always_positive check(year > 0),
 	currval integer not null constraint counter_zero_or_positive check(currval >= 0),
 	primary key (company_id, year)
diff --git a/test/invoice_number_counter.sql b/test/invoice_number_counter.sql
index a2dd262..955c7a0 100644
--- a/test/invoice_number_counter.sql
+++ b/test/invoice_number_counter.sql
@@ -5,7 +5,7 @@ reset client_min_messages;
 
 begin;
 
-select plan(25);
+select plan(27);
 
 set search_path to numerus, auth, public;
 
@@ -19,6 +19,8 @@ select table_privs_are('invoice_number_counter', 'admin', array ['SELECT', 'INSE
 select table_privs_are('invoice_number_counter', 'authenticator', array []::text[]);
 
 select has_column('invoice_number_counter', 'company_id');
+select col_is_fk('invoice_number_counter', 'company_id');
+select fk_ok('invoice_number_counter', 'company_id', 'company', 'company_id');
 select col_type_is('invoice_number_counter', 'company_id', 'integer');
 select col_not_null('invoice_number_counter', 'company_id');
 select col_hasnt_default('invoice_number_counter', 'company_id');
@@ -66,11 +68,6 @@ values (2, 1)
      , (4, 5)
 ;
 
-insert into contact (contact_id, company_id, business_name, vatin, trade_name, phone, email, web, address, city, province, postal_code, country_code)
-values (6, 2, 'Contact 1', 'XX555', '', '777-777-777', 'c@c', '', '', '', '', '', 'ES')
-     , (8, 4, 'Contact 2', 'XX666', '', '888-888-888', 'd@d', '', '', '', '', '', 'ES')
-;
-
 insert into invoice_number_counter (company_id, year, currval)
 values (2, 2010, 6)
      , (2, 2011, 8)