diff --git a/docs/environment.yml b/docs/environment.yml
index acb55ad7b..a036368bf 100644
--- a/docs/environment.yml
+++ b/docs/environment.yml
@@ -15,7 +15,7 @@ dependencies:
   - jupyter_sphinx
   - atomicwrites
   - sphinx_fontawesome
-  - sphinx=2.4.4  # because https://github.com/miyakogi/m2r/pull/55
-  - m2r
+  - sphinx
+  - m2r2
   - pip:
     - sphinx_rtd_theme
diff --git a/docs/source/conf.py b/docs/source/conf.py
index 1d269f271..ab334e5b4 100644
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -53,7 +53,7 @@
     "sphinx.ext.napoleon",
     "jupyter_sphinx.execute",
     "sphinx_fontawesome",
-    "m2r",
+    "m2r2",
 ]
 
 source_parsers = {}