diff --git a/lib/python/README b/lib/python/README
index 077c2547d27ab2868e3337670fb1ddab66820125..ddccc1a21ac839bba55bc2e364a5ef75ebbeb4b3 100644
--- a/lib/python/README
+++ b/lib/python/README
@@ -6,6 +6,10 @@ and your version of Python, and copy it to Makefile.lammps before
 building LAMMPS itself.  You may need to edit one of the provided
 files to match your system.
 
+Note that is not currently possible to use the PYTHON package with
+Python 3, only with Python 2.  The C API changed from Python 2 to 3
+and the LAMMPS code is not compatible with both.
+
 If you create a new Makefile.lammps file suitable for some version of
 Python on some system, that is not a match to one of the provided
 Makefile.lammps.* files, you can send it to the developers, and we can