diff --git a/tests.nix b/tests.nix
index dc85ecb..cb053df 100644
--- a/tests.nix
+++ b/tests.nix
@@ -369,6 +369,21 @@ in
     expected = npins.nixpkgs.outPath;
   };
 
+  introspection.test-follow-sub-npins-with-inputs-input-with-source-arg = {
+    # s: my-lib.inputs.nixpkgs.follows = "with-inputs-dep/nixpkgs" → traverse native inputs
+    expr =
+      (with-inputs
+        {
+          my-lib = mkSrc ./fixtures/fake-flake;
+          with-inputs-dep = mkSrc ./fixtures/with-inputs-flake;
+        }
+        {
+          my-lib = s: { inputs.nixpkgs.follows = "with-inputs-dep/nixpkgs2"; };
+        }
+      ).my-lib.inputs.nixpkgs.outPath;
+    expected = npins.nixpkgs.outPath;
+  };
+
   real-flakes.test-npins-nix-maid-nixosModules-output-is-readable = {
     expr =
       (with-inputs npins { } (inputs: {
diff --git a/with-inputs.nix b/with-inputs.nix
index dedc559..8d300ec 100644
--- a/with-inputs.nix
+++ b/with-inputs.nix
@@ -62,11 +62,9 @@ let
     hostName: subName:
     let
       entry = inputs.${hostName} or null;
+      getSubInput = e: if builtins.isAttrs e && e ? inputs then e.inputs.${subName} or null else null;
     in
-    if entry != null && builtins.isAttrs entry && entry ? inputs then
-      entry.inputs.${subName} or null
-    else
-      null;
+    getSubInput (if builtins.isFunction entry then (entry sources.${hostName}) else entry);
 
   # Resolve an inputs entry to an actual input value, or null if unresolvable.
   # Values with outPath but no _type go through mkInput so their flake.nix is loaded.