diff --git a/benchmarks/basic_commands.py b/benchmarks/basic_commands.py
index ff291a5e3670abb5ef5d79e7cb1819027b16e5fa_YmVuY2htYXJrcy9iYXNpY19jb21tYW5kcy5weQ==..dc48bcc3587db496b485045ea61b154e666a7fb8_YmVuY2htYXJrcy9iYXNpY19jb21tYW5kcy5weQ== 100644
--- a/benchmarks/basic_commands.py
+++ b/benchmarks/basic_commands.py
@@ -51,6 +51,9 @@
         else:
             # pick filename to update
             filename = self.hg('manifest').partition('\n')[0]
+            if not filename:
+                msg = 'no revision checked out in repo: %s' % self.repo_path
+                raise ValueError(msg)
             filename = os.path.join(self.repo_path, filename)
 
         # Do the commits N time