diff --git a/doc/manual/source/conf.py b/doc/manual/source/conf.py
index d30b4d8c0..f93053183 100644
--- a/doc/manual/source/conf.py
+++ b/doc/manual/source/conf.py
@@ -83,7 +83,7 @@ release = "ns-3-dev"
 #
 # 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 = None
 
 # There are two options for replacing |today|: either, you set today to some
 # non-false value, then it is used:
diff --git a/doc/models/source/conf.py b/doc/models/source/conf.py
index 279f85e21..806d96137 100644
--- a/doc/models/source/conf.py
+++ b/doc/models/source/conf.py
@@ -83,7 +83,7 @@ release = "ns-3-dev"
 #
 # 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 = None
 
 # There are two options for replacing |today|: either, you set today to some
 # non-false value, then it is used:
diff --git a/doc/tutorial/source/conf.py b/doc/tutorial/source/conf.py
index 31eb02188..d20defe65 100644
--- a/doc/tutorial/source/conf.py
+++ b/doc/tutorial/source/conf.py
@@ -80,7 +80,7 @@ release = "ns-3-dev"
 #
 # 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 = None
 
 # There are two options for replacing |today|: either, you set today to some
 # non-false value, then it is used: