anchor.diff:  
     src = fetchurl {
       url = "https://computation.llnl.gov/projects/${pname}/download/${pname}-${version}.tar.gz";
  -    sha256 = "19xwi7pz35s2nqgldm6r0jl2k0bs36zhbpnmmzc56s1n3bhzgpw8";
  +    sha256 = "Frd5mex+fyFXqh0Eyh3kojccqBUOBW0klR0MWJZvKoM=";
     };
  -
     patches = [
  -    (fetchurl {
  -      # https://github.com/LLNL/sundials/pull/19
  -      url = "https://github.com/LLNL/sundials/commit/1350421eab6c5ab479de5eccf6af2dcad1eddf30.patch";
  -      sha256 = "0g67lixp9m85fqpb9rzz1hl1z8ibdg0ldwq5z6flj5zl8a7cw52l";
  +    # Fixing an upstream regression in treating cmake prefix directories:
  +    # https://github.com/LLNL/sundials/pull/58
  +    (fetchpatch {
  +      url = "https://github.com/LLNL/sundials/commit/dd32ff9baa05618f36e44aadb420bbae4236ea1e.patch";
  +      sha256 = "kToAuma+2iHFyL1v/l29F3+nug4AdK5cPG6IcXv2afc=";
       })
     ];
   
     cmakeFlags = [
       "-DEXAMPLES_INSTALL_PATH=${placeholder "out"}/share/examples"
     ] ++ stdenv.lib.optionals (lapackSupport) [
  -    "-DLAPACK_ENABLE=ON"
  +    "-DENABLE_LAPACK=ON"
       "-DLAPACK_LIBRARIES=${lapack}/lib/liblapack${stdenv.hostPlatform.extensions.sharedLibrary}"
     ] ++ stdenv.lib.optionals (kluSupport) [
  -    "-DKLU_ENABLE=ON"
  +    "-DENABLE_KLU=ON"
       "-DKLU_INCLUDE_DIR=${suitesparse.dev}/include"
       "-DKLU_LIBRARY_DIR=${suitesparse}/lib"
  -  ] ++ stdenv.lib.optionals (lapackSupport && !lapack.isILP64) [
  -    # Use the correct index type according to lapack which is supposed to be
  -    # the same index type compatible with blas, thanks to the assertion of
  -    # buildInputs
  -    "-DSUNDIALS_INDEX_TYPE=int32_t"
  -  ]
  +  ] ++ [(
  +    # Use the correct index type according to lapack and blas used. They are
  +    # already supposed to be compatible but we check both for extra safety. 64
  +    # should be the default but we prefer to be explicit, for extra safety.
  +    if blas.isILP64 then
  +      "-DSUNDIALS_INDEX_SIZE=64"
  +    else
  +      "-DSUNDIALS_INDEX_SIZE=32"
  +  )]
     ;
   
     doCheck = true;
  
positive.code: 
  stdenv.mkDerivation rec {
    pname = "sundials";
    version = "5.3.0";
  
    buildInputs = [
      python
  
negative.code: { stdenv
  , cmake
  , fetchurl
  , fetchpatch
  , python
  , blas
  , lapack
  