--- a/mercurial/commands.py	Wed Sep 02 15:19:05 2015 -0400
+++ b/mercurial/commands.py	Wed Sep 02 23:50:45 2015 -0400
@@ -3971,6 +3971,7 @@
     section = None
     if name and '.' in name:
         name, section = name.split('.', 1)
+        section = section.lower()
 
     text = help.help_(ui, name, **opts)
 

--- a/tests/test-help.t	Wed Sep 02 15:19:05 2015 -0400
+++ b/tests/test-help.t	Wed Sep 02 23:50:45 2015 -0400
@@ -922,6 +922,10 @@
       "smtp.host"
           Host name of mail server, e.g. "mail.example.com".
   
+Test capitalized section name
+
+  $ hg help scripting.HGPLAIN > /dev/null
+
 Help subsection:
 
   $ hg help config.charsets |grep "Email example:" > /dev/null