Mention GPL version.
diff --git a/docs/license.txt b/docs/license.txt
index 2c6d3ec..876cc4b 100644
--- a/docs/license.txt
+++ b/docs/license.txt
@@ -15,9 +15,10 @@
is suited to products which don't use the GNU General Public
License.
- - The GNU General Public License, found in `GPL.TXT', for programs
- which already use the GPL. Note that the FTL is incompatible with
- the GPL due to its advertisement clause.
+ - The GNU General Public License version 2, found in `GPL.TXT' (any
+ later version can be used also), for programs which already use the
+ GPL. Note that the FTL is incompatible with the GPL due to its
+ advertisement clause.
The contributed PCF driver comes with a license similar to that of the X
Window System. It is compatible to the above two licenses (see file
