diff --git a/lib/modules.nix b/lib/modules.nix
index abcdd1a894cc..0b3560a12661 100644
--- a/lib/modules.nix
+++ b/lib/modules.nix
@@ -113,6 +113,10 @@ rec {
                   args ? {}
                 , # This would be remove in the future, Prefer _module.check option instead.
                   check ? true
+                  # Internal variable to avoid `_key` collisions regardless
+                  # of `extendModules`. Used in `submoduleWith`.
+                  # Test case: lib/tests/modules, "168767"
+                , extensionOffset ? 0
                 }:
     let
       withWarnings = x:
@@ -338,15 +342,17 @@ rec {
         modules ? [],
         specialArgs ? {},
         prefix ? [],
+        extensionOffset ? length modules,
         }:
           evalModules (evalModulesArgs // {
             modules = regularModules ++ modules;
             specialArgs = evalModulesArgs.specialArgs or {} // specialArgs;
             prefix = extendArgs.prefix or evalModulesArgs.prefix;
+            inherit extensionOffset;
           });
 
       type = lib.types.submoduleWith {
-        inherit modules specialArgs;
+        inherit modules specialArgs extensionOffset;
       };
 
       result = withWarnings {
diff --git a/lib/tests/modules.sh b/lib/tests/modules.sh
index 8050c6539fc2..cc13a8d38e37 100755
--- a/lib/tests/modules.sh
+++ b/lib/tests/modules.sh
@@ -293,7 +293,7 @@ checkConfigOutput '^"a c"$' config.result ./functionTo/merging-attrs.nix
 
 # moduleType
 checkConfigOutput '^"a b"$' config.resultFoo ./declare-variants.nix ./define-variant.nix
-checkConfigOutput '^"a y z"$' config.resultFooBar ./declare-variants.nix ./define-variant.nix
+checkConfigOutput '^"a b y z"$' config.resultFooBar ./declare-variants.nix ./define-variant.nix
 checkConfigOutput '^"a b c"$' config.resultFooFoo ./declare-variants.nix ./define-variant.nix
 
 ## emptyValue's
@@ -327,6 +327,10 @@ checkConfigError 'The option .theOption.nested. in .other.nix. is already declar
 # Test that types.optionType leaves types untouched as long as they don't need to be merged
 checkConfigOutput 'ok' config.freeformItems.foo.bar ./adhoc-freeformType-survives-type-merge.nix
 
+# Anonymous submodules don't get nixed by import resolution/deduplication
+# because of an `extendModules` bug, issue 168767.
+checkConfigOutput '^1$' config.sub.specialisation.value ./extendModules-168767-imports.nix
+
 cat <<EOF
 ====== module tests ======
 $pass Pass
diff --git a/lib/tests/modules/extendModules-168767-imports.nix b/lib/tests/modules/extendModules-168767-imports.nix
new file mode 100644
index 000000000000..489e6b5a5d83
--- /dev/null
+++ b/lib/tests/modules/extendModules-168767-imports.nix
@@ -0,0 +1,41 @@
+{ lib
+, extendModules
+, ...
+}:
+with lib;
+{
+  imports = [
+
+    {
+      options.sub = mkOption {
+        default = { };
+        type = types.submodule (
+          { config
+          , extendModules
+          , ...
+          }:
+          {
+            options.value = mkOption {
+              type = types.int;
+            };
+
+            options.specialisation = mkOption {
+              default = { };
+              inherit
+                (extendModules {
+                  modules = [{
+                    specialisation = mkOverride 0 { };
+                  }];
+                })
+                type;
+            };
+          }
+        );
+      };
+    }
+
+    { config.sub.value = 1; }
+
+
+  ];
+}
diff --git a/lib/types.nix b/lib/types.nix
index 5c4b96310617..91b040d24553 100644
--- a/lib/types.nix
+++ b/lib/types.nix
@@ -568,6 +568,11 @@ rec {
       { modules
       , specialArgs ? {}
       , shorthandOnlyDefinesConfig ? false
+
+        # Internal variable to avoid `_key` collisions regardless
+        # of `extendModules`. Wired through by `evalModules`.
+        # Test case: lib/tests/modules, "168767"
+      , extensionOffset ? 0
       }@attrs:
       let
         inherit (lib.modules) evalModules;
@@ -579,11 +584,11 @@ rec {
         allModules = defs: imap1 (n: { value, file }:
           if isFunction value
           then setFunctionArgs
-                (args: lib.modules.unifyModuleSyntax file "${toString file}-${toString n}" (value args))
+                (args: lib.modules.unifyModuleSyntax file "${toString file}-${toString (n + extensionOffset)}" (value args))
                 (functionArgs value)
           else if isAttrs value
           then
-            lib.modules.unifyModuleSyntax file "${toString file}-${toString n}" (shorthandToModule value)
+            lib.modules.unifyModuleSyntax file "${toString file}-${toString (n + extensionOffset)}" (shorthandToModule value)
           else value
         ) defs;
 
@@ -620,6 +625,7 @@ rec {
           (base.extendModules {
             modules = [ { _module.args.name = last loc; } ] ++ allModules defs;
             prefix = loc;
+            extensionOffset = extensionOffset + length defs;
           }).config;
         emptyValue = { value = {}; };
         getSubOptions = prefix: (base.extendModules