diff --git a/installer/data/mysql/kohastructure.sql b/installer/data/mysql/kohastructure.sql
index 4ffbbf2021..a2f3e07dbb 100644
--- a/installer/data/mysql/kohastructure.sql
+++ b/installer/data/mysql/kohastructure.sql
@@ -269,7 +269,7 @@ CREATE TABLE `borrowers` ( -- this table includes information about your patrons
   PRIMARY KEY `borrowernumber` (`borrowernumber`),
   KEY `categorycode` (`categorycode`),
   KEY `branchcode` (`branchcode`),
-  KEY `userid` (`userid`),
+  UNIQUE KEY `userid` (`userid`),
   KEY `guarantorid` (`guarantorid`),
   KEY `surname_idx` (`surname`(255)),
   KEY `firstname_idx` (`firstname`(255)),
diff --git a/installer/data/mysql/updatedatabase.pl b/installer/data/mysql/updatedatabase.pl
index b06142c7a5..1fa6250a13 100755
--- a/installer/data/mysql/updatedatabase.pl
+++ b/installer/data/mysql/updatedatabase.pl
@@ -9608,6 +9608,22 @@ if ( CheckVersion($DBversion) ) {
     SetVersion ($DBversion);
 }
 
+$DBversion = "3.19.00.XXX";
+if ( CheckVersion($DBversion) ) {
+    $dbh->do(q{
+        UPDATE borrowers SET userid = NULL where userid = ""
+    });
+
+    $dbh->do(q{
+        ALTER TABLE borrowers
+            DROP INDEX userid ,
+            ADD UNIQUE userid (userid)
+    });
+
+    print "Upgrade to $DBversion done (Bug 1861 - Unique patrons logins not (totally) enforced)\n";
+    SetVersion($DBversion);
+}
+
 =head1 FUNCTIONS
 
 =head2 TableExists($table)