diff --git a/README.md b/README.md
index 846623d46..2dd4a0945 100644
--- a/README.md
+++ b/README.md
@@ -94,7 +94,8 @@ Starting from September 2022, mavnative, a C extension for parsing mavlink, was
 From the pymavlink directory, you can use :
 
 ```bash
-MDEF=PATH_TO_message_definitions python3 -m pip install . -v
+(cd ..; git clone https://github.com/ArduPilot/mavlink.git)
+MDEF=$PWD/../mavlink/message_definitions python3 -m pip install . -v
 ```
 
 Since pip installation is executed from /tmp, it is necessary to point to the directory containing message definitions with MDEF. MDEF should not be set to any particular message version directory but the parent folder instead. If you have cloned from mavlink/mavlink then this is ```/mavlink/message_definitions``` . Using pip should auto install dependencies and allow you to keep them up-to-date. 
@@ -105,6 +106,21 @@ Or:
 python3 -m pip install .
 ```
 
+## Running the tests
+
+From inside the pymavlink directory, fetch the message definitions alongside
+the checkout and run the suite with `pytest`:
+
+```bash
+(cd ..; git clone https://github.com/ArduPilot/mavlink.git)
+MDEF=$PWD/../mavlink/message_definitions PYTHONPATH=.. python3 -m pytest
+```
+
+`MDEF` points at the message definitions used to generate the dialects; if you
+already have an ArduPilot checkout, point it at that `mavlink/message_definitions`
+instead. `PYTHONPATH=..` imports the local checkout rather than a pip-installed
+copy.
+
 ### Ardupilot Custom Modes
 
 By default, `pymavlink` will map the Ardupilot mode names to mode numbers per the definitions in the [ardupilotmega.xml](https://mavlink.io/en/messages/ardupilotmega.html#PLANE_MODE) file. However, during development, it can be useful to add to or update the default mode mappings.