diff --git a/pkgs/tools/backup/bup/default.nix b/pkgs/tools/backup/bup/default.nix
index 88b3693d7e99..7bea67dc621b 100644
--- a/pkgs/tools/backup/bup/default.nix
+++ b/pkgs/tools/backup/bup/default.nix
@@ -37,6 +37,8 @@ stdenv.mkDerivation {
     "LIBDIR=$(out)/lib/bup"
   ];
 
+  env.NIX_CFLAGS_COMPILE = lib.optionalString stdenv.isDarwin "-Wno-error=implicit-function-declaration";
+
   postInstall = ''
     wrapProgram $out/bin/bup \
       --prefix PATH : ${lib.makeBinPath [ git par2cmdline ]} \