diff --git a/util/db-mysql.sql b/util/db-mysql.sql
index 0267b9c..32cdb52 100644
--- a/util/db-mysql.sql
+++ b/util/db-mysql.sql
@@ -426,7 +426,7 @@
 
 
 create table if not exists `legal_hold` (
-   email varchar(128) default not null
+   email varchar(128) unique not null
 ) Engine=InnoDB;
 
 
diff --git a/util/db-upgrade-1.1.0-vs-1.2.0.sql b/util/db-upgrade-1.1.0-vs-1.2.0.sql
index ed22e5e..45c8e4c 100644
--- a/util/db-upgrade-1.1.0-vs-1.2.0.sql
+++ b/util/db-upgrade-1.1.0-vs-1.2.0.sql
@@ -14,7 +14,7 @@
 create index metadata_idx10 on metadata(`from`);
 
 create table if not exists `legal_hold` (
-   email varchar(128) default not null
+   email varchar(128) unique not null
 ) Engine=InnoDB;