diff --git a/sphinx/themes/agogo/layout.html b/sphinx/themes/agogo/layout.html
index 8bd476cad..f2c880537 100644
--- a/sphinx/themes/agogo/layout.html
+++ b/sphinx/themes/agogo/layout.html
@@ -43,7 +43,7 @@
         </div>
         <div class="sidebar">
           {%- block sidebartoc %}
-          <h3>{{ _('Table Of Contents') }}</h3>
+          <h3>{{ _('Table of Contents') }}</h3>
           {{ toctree() }}
           {%- endblock %}
           {%- block sidebarsearch %}
diff --git a/sphinx/themes/basic/globaltoc.html b/sphinx/themes/basic/globaltoc.html
index dc6fea373..7671a93ca 100644
--- a/sphinx/themes/basic/globaltoc.html
+++ b/sphinx/themes/basic/globaltoc.html
@@ -7,5 +7,5 @@
     :copyright: Copyright 2007-2018 by the Sphinx team, see AUTHORS.
     :license: BSD, see LICENSE for details.
 #}
-<h3><a href="{{ pathto(master_doc) }}">{{ _('Table Of Contents') }}</a></h3>
+<h3><a href="{{ pathto(master_doc) }}">{{ _('Table of Contents') }}</a></h3>
 {{ toctree() }}
diff --git a/sphinx/themes/basic/localtoc.html b/sphinx/themes/basic/localtoc.html
index 5d3c7f4fd..d4cc9e31d 100644
--- a/sphinx/themes/basic/localtoc.html
+++ b/sphinx/themes/basic/localtoc.html
@@ -8,6 +8,6 @@
     :license: BSD, see LICENSE for details.
 #}
 {%- if display_toc %}
-  <h3><a href="{{ pathto(master_doc) }}">{{ _('Table Of Contents') }}</a></h3>
+  <h3><a href="{{ pathto(master_doc) }}">{{ _('Table of Contents') }}</a></h3>
   {{ toc }}
 {%- endif %}
diff --git a/sphinx/themes/haiku/layout.html b/sphinx/themes/haiku/layout.html
index c93c52dbd..c3c79c4d6 100644
--- a/sphinx/themes/haiku/layout.html
+++ b/sphinx/themes/haiku/layout.html
@@ -54,7 +54,7 @@
       <div class="content">
         {#{%- if display_toc %}
         <div id="toc">
-          <h3>{{ _('Table Of Contents') }}</h3>
+          <h3>{{ _('Table of Contents') }}</h3>
           {{ toc }}
         </div>
         {%- endif %}#}
diff --git a/sphinx/themes/scrolls/layout.html b/sphinx/themes/scrolls/layout.html
index 7bb7b19e3..0f9232a00 100644
--- a/sphinx/themes/scrolls/layout.html
+++ b/sphinx/themes/scrolls/layout.html
@@ -38,7 +38,7 @@
       <div id="contentwrapper">
         {%- if display_toc %}
         <div id="toc" role="navigation" aria-label="table of contents navigation">
-          <h3>{{ _('Table Of Contents') }}</h3>
+          <h3>{{ _('Table of Contents') }}</h3>
           {{ toc }}
         </div>
         {%- endif %}
diff --git a/tests/test_theming.py b/tests/test_theming.py
index 8c09271e3..43e97473d 100644
--- a/tests/test_theming.py
+++ b/tests/test_theming.py
@@ -124,7 +124,7 @@ def test_theme_sidebars(app, status, warning):
 
     # test-theme specifies globaltoc and searchbox as default sidebars
     result = (app.outdir / 'index.html').text(encoding='utf8')
-    assert '<h3><a href="#">Table Of Contents</a></h3>' in result
+    assert '<h3><a href="#">Table of Contents</a></h3>' in result
     assert '<h3>Related Topics</h3>' not in result
     assert '<h3>This Page</h3>' not in result
     assert '<h3>Quick search</h3>' in result