diff --git a/treemanifest/__init__.py b/treemanifest/__init__.py
--- a/treemanifest/__init__.py
+++ b/treemanifest/__init__.py
@@ -1001,7 +1001,7 @@
     ('r', 'rev', '', _("revs to prefetch the trees for")),
     ('', 'base', '', _("revs that are assumed to already be local")),
     ] + commands.walkopts, _('--rev REVS PATTERN..'))
-def prefetchtrees(ui, repo, *args, **opts):
+def prefetchtreescmd(ui, repo, *args, **opts):
     revs = repo.revs(opts.get('rev'))
     baserevs = []
     if opts.get('base'):
@@ -1015,9 +1015,19 @@
     for rev in baserevs:
         basemfnodes.add(repo[rev].manifestnode())
 
-    _prefetchtrees(repo, '', mfnodes, basemfnodes, [])
+    prefetchtrees(repo, '', mfnodes, basemfnodes, [])
 
 def _prefetchtrees(repo, rootdir, mfnodes, basemfnodes, directories):
+    '''
+    This is a legacy name for prefetchtrees(), to help transition other modules
+    that call this using the old (private) _prefetchtrees() name.
+
+    This can be deleted once everything has been switched to use the public
+    prefetchtrees() name.
+    '''
+    return prefetchtrees(repo, rootdir, mfnodes, basemfnodes, directories)
+
+def prefetchtrees(repo, rootdir, mfnodes, basemfnodes, directories):
     # If possible, use remotefilelog's more expressive fallbackpath
     if util.safehasattr(repo, 'fallbackpath'):
         fallbackpath = repo.fallbackpath
@@ -1047,16 +1057,12 @@
                             (count, time.time() - start))
 
         if missingnodes:
-            raise error.Abort(_("unable to download %d trees (%s,...)") %
-                               (len(missingnodes), list(missingnodes)[0]))
+            raise MissingNodesError(missingnodes,
+                                    'nodes missing from server response')
     except bundle2.AbortFromPart as exc:
         repo.ui.debug('remote: abort: %s\n' % exc)
         hexnodes = list(hex(mfnode) for mfnode in mfnodes)
-        nodestr = '\n'.join(hexnodes[:10])
-        if len(hexnodes) > 10:
-            nodestr += '\n...'
-        raise error.Abort(_('unable to download the following trees from the '
-                            'server:\n%s') % nodestr, hint=exc.hint)
+        raise MissingNodesError(hexnodes, hint=exc.hint)
     except error.BundleValueError as exc:
         raise error.Abort(_('missing support for %s') % exc)
     finally:
@@ -1220,7 +1226,7 @@
         if not basemfnodes:
             basemfnodes = _findrecenttree(repo, len(repo.changelog) - 1)
 
-        _prefetchtrees(repo, '', mfnodes, basemfnodes, [])
+        prefetchtrees(repo, '', mfnodes, basemfnodes, [])
 
     return result
 
@@ -1471,7 +1477,7 @@
             # Find a recent tree that we already have
             basemfnodes = _findrecenttree(self._repo, linkrev)
 
-        _prefetchtrees(self._repo, name, [node], basemfnodes, [])
+        prefetchtrees(self._repo, name, [node], basemfnodes, [])
         self._shared.markforrefresh()
         return self._shared.get(name, node)
 
@@ -1579,3 +1585,15 @@
             mfl.historystore)
     else:
         orig(self, part)
+
+class MissingNodesError(error.Abort):
+    def __init__(self, nodes, message=None, hint=None):
+        nodestr = '\n'.join(nodes[:10])
+        if len(nodes) > 10:
+            nodestr += '\n...'
+        fullmessage = _(
+            'unable to download the following trees from the server:')
+        if message is not None:
+            fullmessage += ' ' + message
+        fullmessage += '\n' + nodestr
+        super(MissingNodesError, self).__init__(fullmessage, hint=hint)