diff --git a/requirements/constraints.txt b/requirements/constraints.txt
index f25769440752..69ef6a5e23ef 100644
--- a/requirements/constraints.txt
+++ b/requirements/constraints.txt
@@ -100,6 +100,9 @@ docutils<0.18
 # mistune is a dependency of m2r (which is a dependency of sphinxcontrib-openapi)
 # m2r fails to specify the version of mistune that it needs leading to the error message:
 # AttributeError: module 'mistune' has no attribute 'BlockGrammar'
-# https://github.com/miyakogi/m2r/issues/66
+# See Issue: https://github.com/miyakogi/m2r/issues/66
+# m2r is no longer actively maintained: https://github.com/miyakogi/m2r/pull/43
+# This will be fixed when sphinxcontrib-openapi depends on m2r2 instead of m2r
+# See issue: https://github.com/sphinx-contrib/openapi/issues/123
 mistune<2.0.0