Index: simpletest.module
===================================================================
--- simpletest.module	(revision 6455)
+++ simpletest.module	(working copy)
@@ -414,7 +414,7 @@
     // Strip the prefix and skip tables without digits following "simpletest",
     // e.g. {simpletest_test_id}.
     if (preg_match('/simpletest\d+.*/', $table, $matches)) {
-      db_drop_table($ret, $matches[0]);
+      db_query("DROP TABLE %s", $matches[0]);
       $count++;
     }
   }