diff --git a/pkgs/lumpy.nix b/pkgs/lumpy.nix
index e8da265..004ff0b 100644
--- a/pkgs/lumpy.nix
+++ b/pkgs/lumpy.nix
@@ -1,6 +1,6 @@
 { stdenv, lib, fetchFromGitHub, which, autoconf, automake
 , zlib, curl
-, python2, hexdump, sambamba, samblaster, samtools }:
+, python2, python2Packages, hexdump, sambamba, samblaster, samtools }:
 
 stdenv.mkDerivation rec {
   version = "0.3.0";
@@ -39,7 +39,7 @@ stdenv.mkDerivation rec {
     automake
     zlib
     curl
-    (python2.withPackages (packages: with packages; [ numpy pysam ]))
+    (python2.withPackages (packages: with packages; [ python2Packages.numpy pysam ]))
     hexdump
     sambamba
     samblaster