diff --git a/lib/db/mysql.php b/lib/db/mysql.php
index e04e423ff66d2..29244480b5987 100644
--- a/lib/db/mysql.php
+++ b/lib/db/mysql.php
@@ -494,6 +494,10 @@ function main_upgrade($oldversion=0) {
         table_column("course", "", "showgrades", "integer", "2", "unsigned", "1", "", "format");
     }
 
+    if ($oldversion < 2003082101) {
+        execute_sql(" ALTER TABLE `{$CFG->prefix}course` ADD INDEX category (category) ");
+    }
+
     return $result;
 
 }
diff --git a/lib/db/mysql.sql b/lib/db/mysql.sql
index b634f7f7cb2cf..421793cd855cb 100644
--- a/lib/db/mysql.sql
+++ b/lib/db/mysql.sql
@@ -51,7 +51,8 @@ CREATE TABLE `prefix_course` (
   `visible` int(10) unsigned NOT NULL default '1',
   `timecreated` int(10) unsigned NOT NULL default '0',
   `timemodified` int(10) unsigned NOT NULL default '0',
-  PRIMARY KEY  (`id`)
+  PRIMARY KEY  (`id`),
+  KEY `category` (`category`)
 ) TYPE=MyISAM;
 # --------------------------------------------------------
 
diff --git a/lib/db/postgres7.php b/lib/db/postgres7.php
index 4f4f19c6a71f2..e38fdcb01c0bb 100644
--- a/lib/db/postgres7.php
+++ b/lib/db/postgres7.php
@@ -238,6 +238,10 @@ function main_upgrade($oldversion=0) {
         table_column("course", "", "showgrades", "integer", "2", "unsigned", "1", "", "format");
     }
 
+    if ($oldversion < 2003082101) {
+        execute_sql(" CREATE INDEX {$CFG->prefix}course_category_idx ON {$CFG->prefix}course (category) ");
+    }
+
     return $result;
 }
 ?>    
diff --git a/lib/db/postgres7.sql b/lib/db/postgres7.sql
index 1d45f291b3715..a91698bb71346 100644
--- a/lib/db/postgres7.sql
+++ b/lib/db/postgres7.sql
@@ -30,6 +30,8 @@ CREATE TABLE prefix_course (
    timemodified integer NOT NULL default '0'
 );
 
+CREATE INDEX prefix_course_category_idx ON prefix_course (category);
+
 CREATE TABLE prefix_course_categories (
    id SERIAL PRIMARY KEY,
    name varchar(255) NOT NULL default ''