diff --git a/test/invoice_number_counter.sql b/test/invoice_number_counter.sql
index 955c7a0..1bdaafe 100644
--- a/test/invoice_number_counter.sql
+++ b/test/invoice_number_counter.sql
@@ -5,7 +5,7 @@ reset client_min_messages;
 
 begin;
 
-select plan(27);
+select plan(28);
 
 set search_path to numerus, auth, public;
 
@@ -116,11 +116,19 @@ reset role;
 
 select lives_ok( $$
 	insert into invoice_number_counter (company_id, year, currval)
-	values (2, 2008, 0)
+	values (2, 2009, 0)
 	$$,
 	'Should allow starting a counter from zero'
 );
 
+select throws_ok( $$
+	insert into invoice_number_counter (company_id, year, currval)
+	values (2, 2008, -1)
+	$$,
+       '23514', 'new row for relation "invoice_number_counter" violates check constraint "counter_zero_or_positive"',
+	'Should not allow starting a counter from a negative value'
+);
+
 select throws_ok( $$
 	insert into invoice_number_counter (company_id, year, currval)
 	values (2, -2008, 1)