diff --git a/script/sql/create/6.pumps.sql b/script/sql/create/6.pumps.sql
index 1411d9c..c93e88e 100644
--- a/script/sql/create/6.pumps.sql
+++ b/script/sql/create/6.pumps.sql
@@ -10,4 +10,5 @@ create table pumps
 , speed numeric
 , pattern varchar(32) references _pattern(id)
 , check (power is not null or head is not null)
+, check ((power is not null and head is not null) is false)
 );