diff --git a/lib/eval-config.nix b/lib/eval-config.nix
index a0d34b4701f..28db11e45c5 100644
--- a/lib/eval-config.nix
+++ b/lib/eval-config.nix
@@ -61,7 +61,8 @@ rec {
 
   # Optionally check wether all config values have corresponding
   # option declarations.
-  config = pkgs.checker optionDefinitions
-    optionDefinitions.environment.checkConfigurationOptions
-    options optionDefinitions;
+  config =
+    let doCheck = optionDefinitions.environment.checkConfigurationOptions; in
+    assert doCheck -> pkgs.lib.checkModule "" systemModule;
+    systemModule.config;
 }