diff --git a/docs/requirements.txt b/docs/requirements.txt
index bfce308f..069acfde 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -1,8 +1,9 @@
-# Date: 2021/06/26
 # Requirements to build MDTools' documentation.
-# These requirements apply additional to the install requirements of in
-# the root level of MDTools.
+#
+# These requirements apply additionally to the install requirements of
+# MDTools as listed in the requirements file in the root directory of
+# the project.
 
-sphinx >=4.0, <5.0
+sphinx >=3.0, <5.0
 sphinx-rtd-theme >=0.5, <1.0
 readthedocs-sphinx-search >=0.1, <1.0
diff --git a/docs/source/conf.py b/docs/source/conf.py
index 5fc3e554..d3c36c4e 100644
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -102,7 +102,7 @@
 source_suffix = {".rst": "restructuredtext"}
 
 # The document that contains the root toctree directive.
-root_doc = "index"
+master_doc = "index"
 
 # A list of glob-style patterns that should be excluded when looking for
 # source files.  They are matched against the source file names relative
@@ -200,7 +200,7 @@
 default_role = None
 
 # If your documentation needs a minimal Sphinx version, state it here.
-needs_sphinx = "4.0"
+needs_sphinx = "3.0"
 
 # If true, Sphinx will warn about all references where the target cannot
 # be found.
@@ -360,8 +360,8 @@
 
 # latex_documents determines how to group the document tree into LaTeX
 # source files.
-_startdocname = root_doc
 _targetname = htmlhelp_basename + ".tex"
+_startdocname = master_doc
 _title = "MDTools Documentation"
 _author = r" \and ".join(author.split(", "))
 _theme = latex_theme