diff --git a/core/Db/Schema/Myisam.php b/core/Db/Schema/Myisam.php
index cf850e50c3b564e1b76b4af6b39930774bc455c5..c5ecf59875c6e47e6491a852ebdcb442127481d4 100644
--- a/core/Db/Schema/Myisam.php
+++ b/core/Db/Schema/Myisam.php
@@ -185,7 +185,7 @@ class Piwik_Db_Schema_Myisam implements Piwik_Db_Schema_Interface
 							  visitor_days_since_first SMALLINT(5) UNSIGNED NOT NULL,
 							  visit_first_action_time DATETIME NOT NULL,
 							  visit_last_action_time DATETIME NOT NULL,
-							  visit_exit_idaction_url INTEGER(11) UNSIGNED NOT NULL,
+							  visit_exit_idaction_url INTEGER(11) UNSIGNED NULL DEFAULT 0,
 							  visit_exit_idaction_name INTEGER(11) UNSIGNED NOT NULL,
 							  visit_entry_idaction_url INTEGER(11) UNSIGNED NOT NULL,
 							  visit_entry_idaction_name INTEGER(11) UNSIGNED NOT NULL,
@@ -315,7 +315,7 @@ class Piwik_Db_Schema_Myisam implements Piwik_Db_Schema_Interface
 									          server_time DATETIME NOT NULL,
 											  idvisit INTEGER(10) UNSIGNED NOT NULL,
 											  idaction_url INTEGER(10) UNSIGNED DEFAULT NULL,
-											  idaction_url_ref INTEGER(10) UNSIGNED NOT NULL,
+											  idaction_url_ref INTEGER(10) UNSIGNED NULL DEFAULT 0,
 											  idaction_name INTEGER(10) UNSIGNED,
 											  idaction_name_ref INTEGER(10) UNSIGNED NOT NULL,
 											  time_spent_ref_action INTEGER(10) UNSIGNED NOT NULL,