diff --git a/pkgs/development/libraries/fftw/default.nix b/pkgs/development/libraries/fftw/default.nix
index f4b30129e61..4f3d685c1fa 100644
--- a/pkgs/development/libraries/fftw/default.nix
+++ b/pkgs/development/libraries/fftw/default.nix
@@ -3,7 +3,7 @@
 , lib
 , gfortran
 , perl
-, llvmPackages ? null
+, llvmPackages
 , precision ? "double"
 , enableAvx ? stdenv.hostPlatform.avxSupport
 , enableAvx2 ? stdenv.hostPlatform.avx2Support
@@ -11,24 +11,20 @@
 , enableFma ? stdenv.hostPlatform.fmaSupport
 , enableMpi ? false
 , mpi
+, withDoc ? stdenv.cc.isGNU
 }:
 
 with lib;
 
-assert stdenv.cc.isClang -> llvmPackages != null;
 assert elem precision [ "single" "double" "long-double" "quad-precision" ];
 
-let
+stdenv.mkDerivation rec {
+  pname = "fftw-${precision}";
   version = "3.3.10";
-  withDoc = stdenv.cc.isGNU;
-in
-
-stdenv.mkDerivation {
-  name = "fftw-${precision}-${version}";
 
   src = fetchurl {
     urls = [
-      "http://fftw.org/fftw-${version}.tar.gz"
+      "https://fftw.org/fftw-${version}.tar.gz"
       "ftp://ftp.fftw.org/pub/fftw/fftw-${version}.tar.gz"
     ];
     sha256 = "sha256-VskyVJhSzdz6/as4ILAgDHdCZ1vpIXnlnmIVs0DiZGc=";