diff --git a/pkgs/tools/networking/lsh/default.nix b/pkgs/tools/networking/lsh/default.nix
index 77d268f3a47c..5d788af1682e 100644
--- a/pkgs/tools/networking/lsh/default.nix
+++ b/pkgs/tools/networking/lsh/default.nix
@@ -29,6 +29,8 @@ stdenv.mkDerivation rec {
     export lsh_cv_sys_unix98_ptys=yes
   '';
 
+  NIX_CFLAGS_COMPILE = "-std=gnu90";
+
   buildInputs = [ gperf guile gmp zlib liboop readline gnum4 pam ];
 
   meta = {