--- a/mercurial/commands.py	Wed Jul 23 10:50:21 2014 -0500
+++ b/mercurial/commands.py	Wed Jul 23 11:16:22 2014 -0500
@@ -6026,6 +6026,7 @@
         for name, module in extensions.extensions():
             names.append(name)
             vers.append(extensions.moduleversion(module))
-        maxnamelen = max(len(n) for n in names)
-        for i, name in enumerate(names):
-            ui.write("  %-*s  %s\n" % (maxnamelen, name, vers[i]))
+        if names:
+            maxnamelen = max(len(n) for n in names)
+            for i, name in enumerate(names):
+                ui.write("  %-*s  %s\n" % (maxnamelen, name, vers[i]))

--- a/tests/test-extension.t	Wed Jul 23 10:50:21 2014 -0500
+++ b/tests/test-extension.t	Wed Jul 23 11:16:22 2014 -0500
@@ -748,6 +748,17 @@
 Test version number support in 'hg version':
   $ echo '__version__ = (1, 2, 3)' >> throw.py
   $ rm -f throw.pyc throw.pyo
+  $ hg version -v
+  Mercurial Distributed SCM (version *) (glob)
+  (see http://mercurial.selenic.com for more information)
+  
+  Copyright (C) 2005-* Matt Mackall and others (glob)
+  This is free software; see the source for copying conditions. There is NO
+  warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+  
+  Enabled extensions:
+  
+
   $ hg version -v --config extensions.throw=throw.py
   Mercurial Distributed SCM (version *) (glob)
   (see http://mercurial.selenic.com for more information)