diff --git a/pkgs/servers/mail/postfix/default.nix b/pkgs/servers/mail/postfix/default.nix
index cea7eaaab48..6a0ac22602d 100644
--- a/pkgs/servers/mail/postfix/default.nix
+++ b/pkgs/servers/mail/postfix/default.nix
@@ -1,5 +1,7 @@
 {stdenv, fetchurl, db4, glibc}:
 
+assert stdenv.isLinux;
+
 stdenv.mkDerivation {
   name = "postfix-2.2.11";
   src = fetchurl {