diff --git a/pkgs/applications/science/biology/delly/default.nix b/pkgs/applications/science/biology/delly/default.nix
index 2cde00036604..92eda1d1dd13 100644
--- a/pkgs/applications/science/biology/delly/default.nix
+++ b/pkgs/applications/science/biology/delly/default.nix
@@ -4,6 +4,7 @@
 , boost
 , bzip2
 , htslib
+, llvmPackages
 , xz
 , zlib
 , delly
@@ -27,10 +28,11 @@ stdenv.mkDerivation (finalAttrs: {
     htslib
     xz
     zlib
-  ];
+  ] ++ lib.optional stdenv.isDarwin llvmPackages.openmp;
 
   makeFlags = [
     "EBROOTHTSLIB=${htslib}"
+    "PARALLEL=1"
   ];
 
   installPhase = ''