diff --git a/pkgs/tools/networking/libreswan/default.nix b/pkgs/tools/networking/libreswan/default.nix
index 3e7719c40d41..630459f93a9a 100644
--- a/pkgs/tools/networking/libreswan/default.nix
+++ b/pkgs/tools/networking/libreswan/default.nix
@@ -29,6 +29,10 @@ stdenv.mkDerivation rec {
     "-Wno-error=format-truncation"
     "-Wno-error=pointer-compare"
     "-Wno-error=stringop-truncation"
+    # The following flag allows libreswan v3.32 to work with NSS 3.22, see
+    # https://github.com/libreswan/libreswan/issues/334.
+    # This flag should not be needed for libreswan v3.33 (which is not yet released).
+    "-DNSS_PKCS11_2_0_COMPAT=1"
   ];
 
   nativeBuildInputs = [ makeWrapper pkgconfig ];