diff --git a/lang/ghc/files/patch-sphinx-fix.diff b/lang/ghc/files/patch-sphinx-fix.diff
new file mode 100644
index 000000000000..3cfc4c03b6ff
--- /dev/null
+++ b/lang/ghc/files/patch-sphinx-fix.diff
@@ -0,0 +1,27 @@
+https://bugs.gentoo.org/792558
+
+From 83407ffc7acc00cc025b9f6ed063add9ab9f9bcc Mon Sep 17 00:00:00 2001
+From: Krzysztof Gogolewski <krzysztof.gogolewski@tweag.io>
+Date: Fri, 25 Sep 2020 02:52:19 +0200
+Subject: [PATCH] Various documentation fixes
+
+* Use r'' in conf.py. This fixes a Sphinx warning:
+  WARNING: Support for evaluating Python 2 syntax is deprecated and will be removed in Sphinx 4.0. Convert docs/users_guide/conf.py to Python 3 syntax.
+--- docs/users_guide/conf.py
++++ docs/users_guide/conf.py
+@@ -100,13 +100,13 @@ htmlhelp_basename = 'GHCUsersGuide'
+ latex_elements = {
+     'inputenc': '',
+     'utf8extra': '',
+-    'preamble': '''
++    'preamble': r'''
+ \usepackage{fontspec}
+ \usepackage{makeidx}
+ \setsansfont{DejaVu Sans}
+ \setromanfont{DejaVu Serif}
+ \setmonofont{DejaVu Sans Mono}
+-\setlength{\\tymin}{45pt}
++\setlength{\tymin}{45pt}
+ ''',
+ }
+