diff --git a/pkgs/tools/security/knockknock/default.nix b/pkgs/tools/security/knockknock/default.nix
index 2341d2110bf..7cf68d48e18 100644
--- a/pkgs/tools/security/knockknock/default.nix
+++ b/pkgs/tools/security/knockknock/default.nix
@@ -14,6 +14,7 @@ buildPythonPackage rec {
   propagatedBuildInputs = [ pycrypto ];
 
   patchPhase = ''
+    sed -i '/build\//d' setup.py
     substituteInPlace setup.py --replace "/etc" "$out/etc"
     substituteInPlace knockknock.py --replace 'existsInPath("hping3")' '"${hping}/bin/hping3"'
   '';