diff --git a/pkgs/tools/networking/mailutils/default.nix b/pkgs/tools/networking/mailutils/default.nix
index ec76e430ca9..262150e5174 100644
--- a/pkgs/tools/networking/mailutils/default.nix
+++ b/pkgs/tools/networking/mailutils/default.nix
@@ -47,6 +47,7 @@ stdenv.mkDerivation rec {
 
     homepage = http://www.gnu.org/software/mailutils/;
 
-    platforms = stdenv.lib.platforms.all;
+    # Some of the dependencies fail to build on {cyg,dar}win.
+    platforms = stdenv.lib.platforms.gnu;
   };
 }