diff --git a/mod/assignment/db/mysql.php b/mod/assignment/db/mysql.php
index acb78d211be..031f97f0108 100644
--- a/mod/assignment/db/mysql.php
+++ b/mod/assignment/db/mysql.php
@@ -100,11 +100,11 @@ function assignment_upgrade($oldversion) {
     }
 
     if ($oldversion < 2004111200) { 
-        execute_sql('ALTER TABLE prefix_assignment DROP INDEX course;',false);
-        execute_sql('ALTER TABLE prefix_assignment_submissions DROP INDEX assignment;',false);
-        execute_sql('ALTER TABLE prefix_assignment_submissions DROP INDEX userid;',false);
-        execute_sql('ALTER TABLE prefix_assignment_submissions DROP INDEX mailed;',false);
-        execute_sql('ALTER TABLE prefix_assignment_submissions DROP INDEX timemarked;',false);
+        execute_sql("ALTER TABLE {$CFG->prefix}assignment DROP INDEX course;",false);
+        execute_sql("ALTER TABLE {$CFG->prefix}assignment_submissions DROP INDEX assignment;",false);
+        execute_sql("ALTER TABLE {$CFG->prefix}assignment_submissions DROP INDEX userid;",false);
+        execute_sql("ALTER TABLE {$CFG->prefix}assignment_submissions DROP INDEX mailed;",false);
+        execute_sql("ALTER TABLE {$CFG->prefix}assignment_submissions DROP INDEX timemarked;",false);
 
         modify_database('','ALTER TABLE prefix_assignment ADD INDEX course (course);');
         modify_database('','ALTER TABLE prefix_assignment_submissions ADD INDEX assignment(assignment);');
diff --git a/mod/assignment/db/postgres7.php b/mod/assignment/db/postgres7.php
index 58220f34313..4fadbf57376 100644
--- a/mod/assignment/db/postgres7.php
+++ b/mod/assignment/db/postgres7.php
@@ -98,11 +98,11 @@ function assignment_upgrade($oldversion) {
     }
 
     if ($oldversion < 2004111200) { 
-        execute_sql('DROP INDEX prefix_assignment_course_idx;',false);
-        execute_sql('DROP INDEX prefix_assignment_submissions_assignment_idx;',false); 
-        execute_sql('DROP INDEX prefix_assignment_submissions_userid_idx;',false); 
-        execute_sql('DROP INDEX prefix_assignment_submissions_mailed_idx;',false);
-        execute_sql('DROP INDEX prefix_assignment_submissions_timemarked_idx;',false);
+        execute_sql("DROP INDEX {$CFG->prefix}assignment_course_idx;",false);
+        execute_sql("DROP INDEX {$CFG->prefix}assignment_submissions_assignment_idx;",false); 
+        execute_sql("DROP INDEX {$CFG->prefix}assignment_submissions_userid_idx;",false); 
+        execute_sql("DROP INDEX {$CFG->prefix}assignment_submissions_mailed_idx;",false);
+        execute_sql("DROP INDEX {$CFG->prefix}assignment_submissions_timemarked_idx;",false);
 
         modify_database('','CREATE INDEX prefix_assignment_course_idx ON prefix_assignment (course);');
         modify_database('','CREATE INDEX prefix_assignment_submissions_assignment_idx ON prefix_assignment_submissions (assignment);');