diff --git a/pkgs/development/libraries/s2n-tls/default.nix b/pkgs/development/libraries/s2n-tls/default.nix
index 944c3477fbf1..be4b9710533b 100644
--- a/pkgs/development/libraries/s2n-tls/default.nix
+++ b/pkgs/development/libraries/s2n-tls/default.nix
@@ -20,6 +20,7 @@ stdenv.mkDerivation rec {
   cmakeFlags = [
     "-DBUILD_SHARED_LIBS=ON"
     "-DCMAKE_SKIP_BUILD_RPATH=OFF"
+    "-DUNSAFE_TREAT_WARNINGS_AS_ERRORS=OFF" # disable -Werror
   ];
 
   propagatedBuildInputs = [ openssl ]; # s2n-config has find_dependency(LibCrypto).