diff --git a/lib/tests/modules.sh b/lib/tests/modules.sh
index 3950d83f584b..e86b545c4666 100755
--- a/lib/tests/modules.sh
+++ b/lib/tests/modules.sh
@@ -67,6 +67,7 @@ checkConfigOutput '^2$' config.bare-submodule.deep ./declare-bare-submodule.nix
 checkConfigOutput '^42$' config.bare-submodule.nested ./declare-bare-submodule.nix ./declare-bare-submodule-nested-option.nix ./declare-bare-submodule-deep-option.nix ./define-bare-submodule-values.nix
 checkConfigOutput '^420$' config.bare-submodule.deep ./declare-bare-submodule.nix ./declare-bare-submodule-nested-option.nix ./declare-bare-submodule-deep-option.nix ./define-bare-submodule-values.nix
 checkConfigOutput '^2$' config.bare-submodule.deep ./declare-bare-submodule.nix ./declare-bare-submodule-deep-option.nix ./define-shorthandOnlyDefinesConfig-true.nix
+checkConfigError 'The option .bare-submodule.deep. in .*/declare-bare-submodule-deep-option.nix. is already declared in .*/declare-bare-submodule-deep-option-duplicate.nix' config.bare-submodule.deep ./declare-bare-submodule.nix ./declare-bare-submodule-deep-option.nix  ./declare-bare-submodule-deep-option-duplicate.nix
 
 # Check integer types.
 # unsigned
diff --git a/lib/tests/modules/declare-bare-submodule-deep-option-duplicate.nix b/lib/tests/modules/declare-bare-submodule-deep-option-duplicate.nix
new file mode 100644
index 000000000000..06ad1f6e0a51
--- /dev/null
+++ b/lib/tests/modules/declare-bare-submodule-deep-option-duplicate.nix
@@ -0,0 +1,10 @@
+{ lib, ... }:
+let
+  inherit (lib) mkOption types;
+in
+{
+  options.bare-submodule.deep = mkOption {
+    type = types.int;
+    default = 2;
+  };
+}