diff --git a/nixos/modules/security/grsecurity.nix b/nixos/modules/security/grsecurity.nix
index 4eb5c3b990d..f33f7abb52c 100644
--- a/nixos/modules/security/grsecurity.nix
+++ b/nixos/modules/security/grsecurity.nix
@@ -245,11 +245,8 @@ in
             kernel 3.19) to continue.
           '';
         }
-        { assertion = (cfg.stable -> !cfg.testing) || (cfg.testing -> !cfg.stable);
-          message   = ''
-            You must select either the stable or testing patch, not
-            both.
-          '';
+        { assertion = !(cfg.stable && cfg.testing);
+          message   = "Select either one of the stable or testing patch";
         }
         { assertion = (cfg.config.restrictProc -> !cfg.config.restrictProcWithGroup) ||
                       (cfg.config.restrictProcWithGroup -> !cfg.config.restrictProc);