diff --git a/tools/test/topos/opticalUtils.py b/tools/test/topos/opticalUtils.py
index ca01395..e896770 100644
--- a/tools/test/topos/opticalUtils.py
+++ b/tools/test/topos/opticalUtils.py
@@ -6,7 +6,7 @@
 This file contains classes and methods useful for integrating LincOE with Mininet,
 such as startOE, stopOE, LINCLink, and OpticalSwitch
 
-- $ONOS_ROOT ust be set
+- $ONOS_ROOT must be set
 - Need to run with sudo -E to preserve ONOS_ROOT env var
 - We assume LINC-Config-Generator is named LINC-Config-Generator
 - We also assume linc-oe is named linc-oe