diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 9724133..92b03c8 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -32,7 +32,7 @@ jobs:
               bash -x .install-pari.sh
         - name: Local build
           run: |
-            pip install sphinx cython cysignals
+            pip install sphinx>=4.0 cython cysignals
             make build
             make install
             make check
diff --git a/cypari2/closure.pyx b/cypari2/closure.pyx
index 2d5cf1d..0ae7039 100644
--- a/cypari2/closure.pyx
+++ b/cypari2/closure.pyx
@@ -4,7 +4,7 @@ Convert Python functions to PARI closures
 
 AUTHORS:
 
-- Jeroen Demeyer (2015-04-10): initial version, :trac:`18052`.
+- Jeroen Demeyer (2015-04-10): initial version, :sage-gh-issue:`18052`.
 
 Examples:
 
diff --git a/cypari2/gen.pyx b/cypari2/gen.pyx
index 247b1ad..7001de1 100644
--- a/cypari2/gen.pyx
+++ b/cypari2/gen.pyx
@@ -14,27 +14,27 @@ AUTHORS:
   handling.
 
 - Robert Bradshaw, Jeroen Demeyer, William Stein (2010-08-15):
-  Upgrade to PARI 2.4.3 (:trac:`9343`)
+  Upgrade to PARI 2.4.3 (:sage-gh-issue:`9343`)
 
 - Jeroen Demeyer (2011-11-12): rewrite various conversion routines
-  (:trac:`11611`, :trac:`11854`, :trac:`11952`)
+  (:sage-gh-issue:`11611`, :sage-gh-issue:`11854`, :sage-gh-issue:`11952`)
 
 - Peter Bruin (2013-11-17): move Pari to a separate file
-  (:trac:`15185`)
+  (:sage-gh-issue:`15185`)
 
-- Jeroen Demeyer (2014-02-09): upgrade to PARI 2.7 (:trac:`15767`)
+- Jeroen Demeyer (2014-02-09): upgrade to PARI 2.7 (:sage-gh-issue:`15767`)
 
-- Martin von Gagern (2014-12-17): Added some Galois functions (:trac:`17519`)
+- Martin von Gagern (2014-12-17): Added some Galois functions (:sage-gh-issue:`17519`)
 
-- Jeroen Demeyer (2015-01-12): upgrade to PARI 2.8 (:trac:`16997`)
+- Jeroen Demeyer (2015-01-12): upgrade to PARI 2.8 (:sage-gh-issue:`16997`)
 
 - Jeroen Demeyer (2015-03-17): automatically generate methods from
-  ``pari.desc`` (:trac:`17631` and :trac:`17860`)
+  ``pari.desc`` (:sage-gh-issue:`17631` and :sage-gh-issue:`17860`)
 
 - Kiran Kedlaya (2016-03-23): implement infinity type
 
 - Luca De Feo (2016-09-06): Separate Sage-specific components from
-  generic C-interface in ``Pari`` (:trac:`20241`)
+  generic C-interface in ``Pari`` (:sage-gh-issue:`20241`)
 
 - Vincent Delecroix (2017-04-29): Python 3 support and doctest
   conversion
@@ -1618,7 +1618,7 @@ cdef class Gen(Gen_base):
 
         Tests:
 
-        Check that :trac:`16127` has been fixed:
+        Check that :sage-gh-issue:`16127` has been fixed:
 
         >>> pari('1/2') < pari('1/3')
         False
@@ -4041,7 +4041,7 @@ cdef class Gen(Gen_base):
         >>> f()
         [0, 0, 1.00000000000000]
 
-        Variadic closures are supported as well (:trac:`18623`):
+        Variadic closures are supported as well (:sage-gh-issue:`18623`):
 
         >>> f = pari("(v[..])->length(v)")
         >>> f('a', f)
diff --git a/cypari2/handle_error.pyx b/cypari2/handle_error.pyx
index e8c4e82..b7fb712 100644
--- a/cypari2/handle_error.pyx
+++ b/cypari2/handle_error.pyx
@@ -4,9 +4,9 @@ Handling PARI errors
 
 AUTHORS:
 
-- Peter Bruin (September 2013): initial version (:trac:`9640`)
+- Peter Bruin (September 2013): initial version (:sage-gh-issue:`9640`)
 
-- Jeroen Demeyer (January 2015): use ``cb_pari_err_handle`` (:trac:`14894`)
+- Jeroen Demeyer (January 2015): use ``cb_pari_err_handle`` (:sage-gh-issue:`14894`)
 
 """
 
diff --git a/cypari2/pari_instance.pyx b/cypari2/pari_instance.pyx
index 1366ab4..14f4751 100644
--- a/cypari2/pari_instance.pyx
+++ b/cypari2/pari_instance.pyx
@@ -15,23 +15,23 @@ AUTHORS:
   handling.
 
 - Robert Bradshaw, Jeroen Demeyer, William Stein (2010-08-15):
-  Upgrade to PARI 2.4.3 (:trac:`9343`)
+  Upgrade to PARI 2.4.3 (:sage-gh-issue:`9343`)
 
 - Jeroen Demeyer (2011-11-12): rewrite various conversion routines
-  (:trac:`11611`, :trac:`11854`, :trac:`11952`)
+  (:sage-gh-issue:`11611`, :sage-gh-issue:`11854`, :sage-gh-issue:`11952`)
 
 - Peter Bruin (2013-11-17): split off this file from gen.pyx
-  (:trac:`15185`)
+  (:sage-gh-issue:`15185`)
 
-- Jeroen Demeyer (2014-02-09): upgrade to PARI 2.7 (:trac:`15767`)
+- Jeroen Demeyer (2014-02-09): upgrade to PARI 2.7 (:sage-gh-issue:`15767`)
 
-- Jeroen Demeyer (2014-09-19): upgrade to PARI 2.8 (:trac:`16997`)
+- Jeroen Demeyer (2014-09-19): upgrade to PARI 2.8 (:sage-gh-issue:`16997`)
 
 - Jeroen Demeyer (2015-03-17): automatically generate methods from
-  ``pari.desc`` (:trac:`17631` and :trac:`17860`)
+  ``pari.desc`` (:sage-gh-issue:`17631` and :sage-gh-issue:`17860`)
 
 - Luca De Feo (2016-09-06): Separate Sage-specific components from
-  generic C-interface in ``Pari`` (:trac:`20241`)
+  generic C-interface in ``Pari`` (:sage-gh-issue:`20241`)
 
 Examples:
 
@@ -226,7 +226,7 @@ Check that the documentation is generated correctly:
 'The constant :math:`\\pi` ...'
 
 Check that output from PARI's print command is actually seen by
-Python (:trac:`9636`):
+Python (:sage-gh-issue:`9636`):
 
 >>> pari('print("test")')
 test
@@ -1049,7 +1049,7 @@ cdef class Pari(Pari_auto):
         >>> pari = cypari2.Pari()
         >>> pari.init_primes(200000)
 
-        We make sure that ticket :trac:`11741` has been fixed:
+        We make sure that ticket :sage-gh-issue:`11741` has been fixed:
 
         >>> pari.init_primes(2**30)
         Traceback (most recent call last):
diff --git a/cypari2/paridecl.pxd b/cypari2/paridecl.pxd
index bc46768..e5c9eef 100644
--- a/cypari2/paridecl.pxd
+++ b/cypari2/paridecl.pxd
@@ -12,13 +12,13 @@ AUTHORS:
  - (unknown authors before 2010)
 
  - Robert Bradshaw, Jeroen Demeyer, William Stein (2010-08-15):
-   Upgrade to PARI 2.4.3 (:trac:`9343`)
+   Upgrade to PARI 2.4.3 (:sage-gh-issue:`9343`)
 
- - Jeroen Demeyer (2010-08-15): big clean up (:trac:`9898`)
+ - Jeroen Demeyer (2010-08-15): big clean up (:sage-gh-issue:`9898`)
 
- - Jeroen Demeyer (2014-02-09): upgrade to PARI 2.7 (:trac:`15767`)
+ - Jeroen Demeyer (2014-02-09): upgrade to PARI 2.7 (:sage-gh-issue:`15767`)
 
- - Jeroen Demeyer (2014-09-19): upgrade to PARI 2.8 (:trac:`16997`)
+ - Jeroen Demeyer (2014-09-19): upgrade to PARI 2.8 (:sage-gh-issue:`16997`)
 """
 
 #*****************************************************************************
diff --git a/docs/source/conf.py b/docs/source/conf.py
index 9e0a9c9..463fc77 100644
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -25,7 +25,7 @@
 
 # If your documentation needs a minimal Sphinx version, state it here.
 #
-needs_sphinx = '1.6'
+needs_sphinx = '4.0'
 
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
@@ -68,7 +68,7 @@
 #
 # This is also used if you do content translation via gettext catalogs.
 # Usually you set "language" from the command line for these cases.
-language = None
+language = 'en'
 
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
@@ -160,15 +160,14 @@
 
 # Links to external resources (copied from Sage)
 extlinks = {
-    'trac': ('https://trac.sagemath.org/%s', 'Sage ticket #'),
-    'wikipedia': ('https://en.wikipedia.org/wiki/%s', 'Wikipedia article '),
-    'arxiv': ('http://arxiv.org/abs/%s', 'Arxiv '),
-    'oeis': ('https://oeis.org/%s', 'OEIS sequence '),
-    'doi': ('https://dx.doi.org/%s', 'doi:'),
-    'pari': ('http://pari.math.u-bordeaux.fr/dochtml/help/%s', 'pari:'),
-    'mathscinet': ('http://www.ams.org/mathscinet-getitem?mr=%s', 'MathSciNet ')
-    }
-
+    'sage-gh-issue': ('https://github.com/sagemath/sage/issues/%s', 'sage github issue #%s'),
+    'wikipedia': ('https://en.wikipedia.org/wiki/%s', 'Wikipedia article %s'),
+    'arxiv': ('https://arxiv.org/abs/%s', 'arXiv %s'),
+    'oeis': ('https://oeis.org/%s', 'OEIS sequence %s'),
+    'doi': ('https://doi.org/%s', 'doi:%s'),
+    'pari': ('https://pari.math.u-bordeaux.fr/dochtml/help/%s', 'pari:%s'),
+    'mathscinet': ('https://www.ams.org/mathscinet-getitem?mr=%s', 'MathSciNet %s')
+}
 
 # Monkey-patch inspect with Cython support
 def isfunction(obj):