diff --git a/doc/gendoc.py b/doc/gendoc.py
--- a/doc/gendoc.py
+++ b/doc/gendoc.py
@@ -196,6 +196,12 @@
             return help.registrar.command.CATEGORY_NONE
         return helpcategory
 
+    # Keep a log of processed commands. If a command category isn't registered
+    # in help.CATEGORY_ORDER, the command doesn't get processed by
+    # commandprinter. By comparing the list of processed commands to the
+    # original list of commands, we can detect unregistered categories.
+    processedcmds = []
+
     # Print the help for each command. We present the commands grouped by
     # category, and we use help.CATEGORY_ORDER as a guide for a helpful order
     # in which to present the categories.
@@ -216,6 +222,7 @@
         for f in sorted(categorycmds):
             if f.startswith(b"debug"):
                 continue
+            processedcmds.append(f)  # log command
             d = get_cmd(h[f], cmdtable)
             ui.write(sectionfunc(d[b'cmd']))
             # short description
@@ -251,7 +258,17 @@
             # aliases
             if d[b'aliases']:
                 ui.write(_(b"    aliases: %s\n\n") % b" ".join(d[b'aliases']))
-
+    # Make sure that we left no commands unprocessed.
+    expected = sorted(filter(lambda c: not c.startswith('debug'), cmds))
+    observed = sorted(processedcmds)
+    if not observed == expected:
+        unprocessed = sorted(set(expected) - set(observed))
+        unprocessedinfo = ', '.join(
+            "%s (%s)" % (cmd, helpcategory(cmd))
+            for cmd in unprocessed
+        )
+        raise AssertionError("The following commands did not register their"
+            " (category) in help.CATEGORY_ORDER: %s" % unprocessedinfo)
 
 def allextensionnames():
     return set(extensions.enabled().keys()) | set(extensions.disabled().keys())