diff --git a/etc/schema/mysql/mysql.schema.sql b/etc/schema/mysql/mysql.schema.sql
index d211379b..58d63f4f 100644
--- a/etc/schema/mysql/mysql.schema.sql
+++ b/etc/schema/mysql/mysql.schema.sql
@@ -513,7 +513,7 @@ CREATE TABLE comment (
   environment_id binary(20) NOT NULL COMMENT 'environment.id',
 
   object_type enum('host', 'service') NOT NULL,
-  host_id binary(20) DEFAULT NULL COMMENT 'host.id',
+  host_id binary(20) NOT NULL COMMENT 'host.id',
   service_id binary(20) DEFAULT NULL COMMENT 'service.id',
 
   name_checksum binary(20) NOT NULL COMMENT 'sha1(name)',
@@ -539,7 +539,7 @@ CREATE TABLE downtime (
 
   triggered_by_id binary(20) DEFAULT NULL COMMENT 'downtime.id',
   object_type enum('host', 'service') NOT NULL,
-  host_id binary(20) DEFAULT NULL COMMENT 'host.id',
+  host_id binary(20) NOT NULL COMMENT 'host.id',
   service_id binary(20) DEFAULT NULL COMMENT 'service.id',
 
   name_checksum binary(20) NOT NULL COMMENT 'sha1(name)',