diff --git a/api/src/opentrons/hardware_control/controller.py b/api/src/opentrons/hardware_control/controller.py
index <HASH>..<HASH> 100644
--- a/api/src/opentrons/hardware_control/controller.py
+++ b/api/src/opentrons/hardware_control/controller.py
@@ -41,7 +41,9 @@ class Controller:
                 'This is intended to run on a robot, and while it can connect '
                 'to a smoothie via a usb/serial adapter unexpected things '
                 'using gpios (such as smoothie reset or light management) '
-                'will fail')
+                'will fail. If you are seeing this message and you are '
+                'running on a robot, you need to set the RUNNING_ON_PI '
+                'environmental variable to 1.')
 
         self.config = config or opentrons.config.robot_configs.load()
feat(api): add info to debug warning on how IS_ROBOT is determined (#<I>)

If you run a robot without RUNNING_ON_PI in the environment you get this warning message (and substantially reduced functionality), but it is not clear how to resolve it. This provides that information. In my case it was because I was invoking one Python script from another with subprocess.