diff --git a/doc/HACKING.md b/doc/HACKING.md
index 92569a5c8..a391f3297 100644
--- a/doc/HACKING.md
+++ b/doc/HACKING.md
@@ -213,7 +213,7 @@ There are three kinds of tests:
 * **blackbox tests** - These tests setup a mini-regtest environment and test
   lightningd as a whole.  They can be run individually:
 
-  `PYTHONPATH=contrib/pylightning:contrib/pyln-client:contrib/pyln-testing py.test -v tests/`
+  `PYTHONPATH=contrib/pylightning:contrib/pyln-client:contrib/pyln-testing:contrib/pyln-proto py.test -v tests/`
 
   You can also append `-k TESTNAME` to run a single test.  Environment variables
   `DEBUG_SUBD=<subdaemon>` and `TIMEOUT=<seconds>` can be useful for debugging