diff --git a/tests/test-treemanifest-prefetch.t b/tests/test-treemanifest-prefetch.t
--- a/tests/test-treemanifest-prefetch.t
+++ b/tests/test-treemanifest-prefetch.t
@@ -493,3 +493,10 @@
   $ hg prefetch
   0 trees fetched over * (glob)
 #endif
+
+Running prefetch in the master repository should fail gracefully
+
+  $ cd ../master
+  $ hg prefetch
+  abort: no remote server configured to fetch trees from
+  [255]
diff --git a/treemanifest/__init__.py b/treemanifest/__init__.py
--- a/treemanifest/__init__.py
+++ b/treemanifest/__init__.py
@@ -1274,7 +1274,11 @@
     if util.safehasattr(repo, 'fallbackpath'):
         return repo.fallbackpath
     else:
-        return repo.ui.config('paths', 'default')
+        path = repo.ui.config('paths', 'default')
+        if not path:
+            raise error.Abort(
+                "no remote server configured to fetch trees from")
+        return path
 
 def pull(orig, ui, repo, *pats, **opts):
     # If we're not in treeonly mode, and we're missing public commits from the