diff --git a/README.md b/README.md
index af72ae7..9731329 100644
--- a/README.md
+++ b/README.md
@@ -11,6 +11,8 @@ See http://furrtek.free.fr/index.php?a=esl for more details.
 
 ## Tools
 
+Use Python 2. Python 3 may work but Pyserial isn't happy in some cases.
+
 * img2dm.py: Sends an image to a dot matrix ESL. Run without parameters for usage.
 * rawcmd.py: Send arbitrary data to ESL.
 * flashtest.py: Test tool to program remote control frame in ESL Blaster (more work needed...).