diff --git a/pkgs/tools/networking/p2p/tahoe-lafs/default.nix b/pkgs/tools/networking/p2p/tahoe-lafs/default.nix
index 836f3e1e60ca..1f935c2f83b0 100644
--- a/pkgs/tools/networking/p2p/tahoe-lafs/default.nix
+++ b/pkgs/tools/networking/p2p/tahoe-lafs/default.nix
@@ -32,12 +32,12 @@ buildPythonPackage rec {
   '';
 
   # Some tests want this + http://tahoe-lafs.org/source/tahoe-lafs/deps/tahoe-dep-sdists/mock-0.6.0.tar.bz2
-  buildInputs = [ unzip numpy mock ];
+  buildInputs = [ unzip numpy ];
 
   # The `backup' command requires `sqlite3'.
   propagatedBuildInputs =
     [ twisted foolscap nevow simplejson zfec pycryptopp sqlite3
-      darcsver setuptoolsTrial setuptoolsDarcs pycrypto pyasn1 zope_interface
+      darcsver setuptoolsTrial setuptoolsDarcs pycrypto pyasn1 zope_interface mock
     ];
 
   postInstall = ''