diff --git a/crates/perry-runtime/src/object/global_this.rs b/crates/perry-runtime/src/object/global_this.rs
index 0d9c621145..5c47560502 100644
--- a/crates/perry-runtime/src/object/global_this.rs
+++ b/crates/perry-runtime/src/object/global_this.rs
@@ -985,7 +985,7 @@ extern "C" fn global_this_queue_microtask_thunk(
 /// Tag detection uses the same coarse NaN-box / GC-type discrimination
 /// the rest of the runtime relies on: arrays → `"[object Array]"`,
 /// strings → `"[object String]"`, null/undefined → matching tags,
-/// numbers/bools → primitive tags, generic objects/closures →
+/// numbers/bools/functions → primitive/builtin tags, generic objects →
 /// `"[object Object]"`.
 ///
 /// Unblocks ramda's `_isArguments.js` IIFE which evaluates
@@ -1780,6 +1780,11 @@ fn set_intrinsic_to_string_tag(obj: *mut ObjectHeader, tag: &str) {
             f64::from_bits(crate::js_nanbox_string(tag_str as i64).to_bits()),
         );
     }
+    crate::symbol::set_symbol_property_attrs(
+        obj as usize,
+        sym as usize,
+        super::PropertyAttrs::new(false, false, true),
+    );
 }
 
 /// Build a `TypeError` value for a `%Generator.prototype%` method invoked on a
@@ -2545,9 +2550,18 @@ pub(crate) fn populate_global_this_builtins(singleton: *mut ObjectHeader) {
             // gated on the AST shape and never read these fields. Math uses the
             // richer install that also exposes per-method name/length descriptors.
             match name {
-                "Math" => install_math_namespace(ns_obj),
-                "JSON" => install_json_namespace_members(ns_obj),
-                "Reflect" => install_reflect_namespace_members(ns_obj),
+                "Math" => {
+                    install_math_namespace(ns_obj);
+                    set_intrinsic_to_string_tag(ns_obj, "Math");
+                }
+                "JSON" => {
+                    install_json_namespace_members(ns_obj);
+                    set_intrinsic_to_string_tag(ns_obj, "JSON");
+                }
+                "Reflect" => {
+                    install_reflect_namespace_members(ns_obj);
+                    set_intrinsic_to_string_tag(ns_obj, "Reflect");
+                }
                 "Atomics" => install_atomics_namespace_members(ns_obj),
                 "Intl" => crate::intl::install_intl_namespace(ns_obj),
                 _ => {}
diff --git a/crates/perry-runtime/src/object/mod.rs b/crates/perry-runtime/src/object/mod.rs
index a6a3720dbc..00e1a89616 100644
--- a/crates/perry-runtime/src/object/mod.rs
+++ b/crates/perry-runtime/src/object/mod.rs
@@ -1912,6 +1912,21 @@ pub unsafe extern "C" fn js_object_to_string(value: f64) -> f64 {
         let str_ptr = crate::string::js_string_from_bytes(bytes.as_ptr(), bytes.len() as u32);
         return f64::from_bits(STRING_TAG | (str_ptr as u64 & POINTER_MASK));
     }
+    if (raw_addr >= 0x10000 && crate::closure::is_closure_ptr(raw_addr))
+        || crate::object::is_class_object_ptr(raw_addr as *const u8)
+    {
+        let bytes = b"[object Function]";
+        let str_ptr = crate::string::js_string_from_bytes(bytes.as_ptr(), bytes.len() as u32);
+        return f64::from_bits(STRING_TAG | (str_ptr as u64 & POINTER_MASK));
+    }
+    if jsv.is_int32() {
+        let class_id = (bits & 0xFFFF_FFFF) as u32;
+        if crate::object::is_class_id_registered(class_id) {
+            let bytes = b"[object Function]";
+            let str_ptr = crate::string::js_string_from_bytes(bytes.as_ptr(), bytes.len() as u32);
+            return f64::from_bits(STRING_TAG | (str_ptr as u64 & POINTER_MASK));
+        }
+    }
     if jsv.is_int32() || jsv.is_number() {
         let bytes = b"[object Number]";
         let str_ptr = crate::string::js_string_from_bytes(bytes.as_ptr(), bytes.len() as u32);
diff --git a/test-parity/node-suite/globals/object-tostring-brands.ts b/test-parity/node-suite/globals/object-tostring-brands.ts
new file mode 100644
index 0000000000..6251bd4550
--- /dev/null
+++ b/test-parity/node-suite/globals/object-tostring-brands.ts
@@ -0,0 +1,35 @@
+function ordinary() {}
+const arrow = () => {};
+class Klass {}
+
+for (const [label, value] of [
+  ["ordinary", ordinary],
+  ["arrow", arrow],
+  ["class", Klass],
+  ["Array", Array],
+  ["Math.max", Math.max],
+  ["Math", Math],
+  ["JSON", JSON],
+  ["Reflect", Reflect],
+] as const) {
+  console.log(label + ":", Object.prototype.toString.call(value));
+}
+
+for (const [label, value] of [
+  ["Math", Math],
+  ["JSON", JSON],
+  ["Reflect", Reflect],
+] as const) {
+  const desc = Object.getOwnPropertyDescriptor(value, Symbol.toStringTag);
+  const rendered = desc
+    ? JSON.stringify([desc.value, desc.writable, desc.enumerable, desc.configurable])
+    : "missing";
+  console.log(label + " tag desc:", rendered);
+}
+
+ordinary[Symbol.toStringTag] = "CallableOverride";
+console.log("function override:", Object.prototype.toString.call(ordinary));
+
+const namespaceOverride = Object.create(Math);
+Object.defineProperty(namespaceOverride, Symbol.toStringTag, { value: "NamespaceOverride" });
+console.log("namespace override:", Object.prototype.toString.call(namespaceOverride));