diff --git a/treemanifest/__init__.py b/treemanifest/__init__.py
--- a/treemanifest/__init__.py
+++ b/treemanifest/__init__.py
@@ -999,23 +999,20 @@
 
 @command('prefetchtrees', [
     ('r', 'rev', '', _("revs to prefetch the trees for")),
-    ('', 'base', '', _("revs that are assumed to already be local")),
+    ('b', 'base', '', _("rev that is assumed to already be local")),
     ] + commands.walkopts, _('--rev REVS PATTERN..'))
 def prefetchtrees(ui, repo, *args, **opts):
     revs = repo.revs(opts.get('rev'))
-    baserevs = []
-    if opts.get('base'):
-        baserevs = repo.revs(opts.get('base'))
-
     mfnodes = set()
     for rev in revs:
         mfnodes.add(repo[rev].manifestnode())
 
-    basemfnodes = set()
-    for rev in baserevs:
-        basemfnodes.add(repo[rev].manifestnode())
+    basemfnode = set()
+    base = opts.get('base')
+    if base:
+        basemfnode.add(repo[base].manifestnode())
 
-    _prefetchtrees(repo, '', mfnodes, basemfnodes, [])
+    _prefetchtrees(repo, '', mfnodes, basemfnode, [])
 
 def _prefetchtrees(repo, rootdir, mfnodes, basemfnodes, directories):
     # If possible, use remotefilelog's more expressive fallbackpath