diff --git a/README.md b/README.md
index 1d1ca677b096d7f3db04c11175ad50007bd4266d..0135539a85af8c5983deebf9ab583eeac285e1c6 100644
--- a/README.md
+++ b/README.md
@@ -30,6 +30,12 @@ Run the following:
 
     pip install .
 
+or
+
+    pip install .[gssapi]
+
+to also install the optional dependency `gssapi`.
+
 ### Usage
 
 To use python-nbxmpp, `import nbxmpp` in your application.
diff --git a/setup.cfg b/setup.cfg
index b6ca9ff2a6d090c8a727ca0e59ef05d36802c6fe..a6c3da93743fba6d8d82e47fa7c51ddaef6317b4 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -4,7 +4,7 @@ version = 3.0.0-dev2
 description = XMPP Library
 author = Yann Leboulanger, Philipp Hoerist
 author_email = gajim-devel@gajim.org
-long_description = file: README.md  
+long_description = file: README.md
 long_description_content_type = text/markdown
 keywords = xmpp chat
 url = https://dev.gajim.org/gajim/python-nbxmpp
@@ -20,6 +20,9 @@ install_requires =
     precis-i18n>=1.0.0
     idna
 
+[options.extras_require]
+gssapi = gssapi
+
 [options.packages.find]
 exclude =
     test*