diff --git a/src/js/internal/streams/native-readable.ts b/src/js/internal/streams/native-readable.ts
index 65307212b821..c9e960c75775 100644
--- a/src/js/internal/streams/native-readable.ts
+++ b/src/js/internal/streams/native-readable.ts
@@ -66,7 +66,9 @@ function constructNativeReadable(readableStream: ReadableStream, options): Nativ
     stream.debugId = ++debugId;
   }
 
-  stream.$bunNativePtr = bunNativePtr;
+  // Define the own property directly: an ordinary put would walk the prototype
+  // chain, which user code can graft onto ReadableStream.prototype's accessors.
+  $putByIdDirectPrivate(stream, "bunNativePtr", bunNativePtr);
   stream[kRefCount] = 0;
   stream[kConstructed] = false;
   stream[kPendingRead] = false;
diff --git a/src/jsc/bindings/webcore/streams/JSReadableStream.cpp b/src/jsc/bindings/webcore/streams/JSReadableStream.cpp
index d3d81565f422..007dc119037f 100644
--- a/src/jsc/bindings/webcore/streams/JSReadableStream.cpp
+++ b/src/jsc/bindings/webcore/streams/JSReadableStream.cpp
@@ -786,48 +786,78 @@ JSC_DEFINE_HOST_FUNCTION(jsReadableStreamPrototypeFunction_blob, (JSGlobalObject
 }
 
 // Bun private-name accessors ($bunNativePtr / $bunNativeType / $disturbed).
+// JSC brand-checks DOMAttribute getters (PropertySlot::customGetter) but invokes
+// custom setters with any receiver inheriting the accessor, so each one validates
+// thisValue itself.
 
-JSC_DEFINE_CUSTOM_GETTER(jsReadableStreamPrototype_nativePtrGetter, (JSGlobalObject*, JSC::EncodedJSValue thisValue, PropertyName))
+JSC_DEFINE_CUSTOM_GETTER(jsReadableStreamPrototype_nativePtrGetter, (JSGlobalObject * lexicalGlobalObject, JSC::EncodedJSValue thisValue, PropertyName propertyName))
 {
-    auto* stream = uncheckedDowncast<JSReadableStream>(JSValue::decode(thisValue));
+    auto& vm = JSC::getVM(lexicalGlobalObject);
+    auto scope = DECLARE_THROW_SCOPE(vm);
+    auto* stream = dynamicDowncast<JSReadableStream>(JSValue::decode(thisValue));
+    if (!stream) [[unlikely]]
+        return throwVMDOMAttributeGetterTypeError(lexicalGlobalObject, scope, JSReadableStream::info(), propertyName);
     JSValue nativePtr = stream->nativePtrForJS();
     return JSValue::encode(nativePtr.isEmpty() ? jsUndefined() : nativePtr);
 }
 
-JSC_DEFINE_CUSTOM_SETTER(jsReadableStreamPrototype_nativePtrSetter, (JSGlobalObject * lexicalGlobalObject, JSC::EncodedJSValue thisValue, JSC::EncodedJSValue encodedValue, PropertyName))
+JSC_DEFINE_CUSTOM_SETTER(jsReadableStreamPrototype_nativePtrSetter, (JSGlobalObject * lexicalGlobalObject, JSC::EncodedJSValue thisValue, JSC::EncodedJSValue encodedValue, PropertyName propertyName))
 {
     auto& vm = JSC::getVM(lexicalGlobalObject);
-    auto* stream = uncheckedDowncast<JSReadableStream>(JSValue::decode(thisValue));
+    auto scope = DECLARE_THROW_SCOPE(vm);
+    auto* stream = dynamicDowncast<JSReadableStream>(JSValue::decode(thisValue));
+    if (!stream) [[unlikely]] {
+        throwDOMAttributeSetterTypeError(lexicalGlobalObject, scope, JSReadableStream::info(), propertyName);
+        return false;
+    }
     stream->m_nativePtr.set(vm, stream, JSValue::decode(encodedValue));
     return true;
 }
 
-JSC_DEFINE_CUSTOM_GETTER(jsReadableStreamPrototype_nativeTypeGetter, (JSGlobalObject*, JSC::EncodedJSValue thisValue, PropertyName))
+JSC_DEFINE_CUSTOM_GETTER(jsReadableStreamPrototype_nativeTypeGetter, (JSGlobalObject * lexicalGlobalObject, JSC::EncodedJSValue thisValue, PropertyName propertyName))
 {
-    const auto* stream = uncheckedDowncast<JSReadableStream>(JSValue::decode(thisValue));
+    auto& vm = JSC::getVM(lexicalGlobalObject);
+    auto scope = DECLARE_THROW_SCOPE(vm);
+    const auto* stream = dynamicDowncast<JSReadableStream>(JSValue::decode(thisValue));
+    if (!stream) [[unlikely]]
+        return throwVMDOMAttributeGetterTypeError(lexicalGlobalObject, scope, JSReadableStream::info(), propertyName);
     return JSValue::encode(jsNumber(stream->m_nativeType));
 }
 
-JSC_DEFINE_CUSTOM_SETTER(jsReadableStreamPrototype_nativeTypeSetter, (JSGlobalObject * lexicalGlobalObject, JSC::EncodedJSValue thisValue, JSC::EncodedJSValue encodedValue, PropertyName))
+JSC_DEFINE_CUSTOM_SETTER(jsReadableStreamPrototype_nativeTypeSetter, (JSGlobalObject * lexicalGlobalObject, JSC::EncodedJSValue thisValue, JSC::EncodedJSValue encodedValue, PropertyName propertyName))
 {
     auto& vm = JSC::getVM(lexicalGlobalObject);
     auto scope = DECLARE_THROW_SCOPE(vm);
-    auto* stream = uncheckedDowncast<JSReadableStream>(JSValue::decode(thisValue));
+    auto* stream = dynamicDowncast<JSReadableStream>(JSValue::decode(thisValue));
+    if (!stream) [[unlikely]] {
+        throwDOMAttributeSetterTypeError(lexicalGlobalObject, scope, JSReadableStream::info(), propertyName);
+        return false;
+    }
     int32_t nativeType = JSValue::decode(encodedValue).toInt32(lexicalGlobalObject);
     RETURN_IF_EXCEPTION(scope, false);
     stream->m_nativeType = nativeType;
     return true;
 }
 
-JSC_DEFINE_CUSTOM_GETTER(jsReadableStreamPrototype_disturbedGetter, (JSGlobalObject*, JSC::EncodedJSValue thisValue, PropertyName))
+JSC_DEFINE_CUSTOM_GETTER(jsReadableStreamPrototype_disturbedGetter, (JSGlobalObject * lexicalGlobalObject, JSC::EncodedJSValue thisValue, PropertyName propertyName))
 {
-    const auto* stream = uncheckedDowncast<JSReadableStream>(JSValue::decode(thisValue));
+    auto& vm = JSC::getVM(lexicalGlobalObject);
+    auto scope = DECLARE_THROW_SCOPE(vm);
+    const auto* stream = dynamicDowncast<JSReadableStream>(JSValue::decode(thisValue));
+    if (!stream) [[unlikely]]
+        return throwVMDOMAttributeGetterTypeError(lexicalGlobalObject, scope, JSReadableStream::info(), propertyName);
     return JSValue::encode(jsBoolean(stream->m_disturbed));
 }
 
-JSC_DEFINE_CUSTOM_SETTER(jsReadableStreamPrototype_disturbedSetter, (JSGlobalObject * lexicalGlobalObject, JSC::EncodedJSValue thisValue, JSC::EncodedJSValue encodedValue, PropertyName))
+JSC_DEFINE_CUSTOM_SETTER(jsReadableStreamPrototype_disturbedSetter, (JSGlobalObject * lexicalGlobalObject, JSC::EncodedJSValue thisValue, JSC::EncodedJSValue encodedValue, PropertyName propertyName))
 {
-    auto* stream = uncheckedDowncast<JSReadableStream>(JSValue::decode(thisValue));
+    auto& vm = JSC::getVM(lexicalGlobalObject);
+    auto scope = DECLARE_THROW_SCOPE(vm);
+    auto* stream = dynamicDowncast<JSReadableStream>(JSValue::decode(thisValue));
+    if (!stream) [[unlikely]] {
+        throwDOMAttributeSetterTypeError(lexicalGlobalObject, scope, JSReadableStream::info(), propertyName);
+        return false;
+    }
     stream->m_disturbed = JSValue::decode(encodedValue).toBoolean(lexicalGlobalObject);
     return true;
 }
diff --git a/test/js/node/stream/node-stream.test.js b/test/js/node/stream/node-stream.test.js
index 0bc56bd5fc87..a0f76e1ce77c 100644
--- a/test/js/node/stream/node-stream.test.js
+++ b/test/js/node/stream/node-stream.test.js
@@ -388,6 +388,41 @@ it("Readable.fromWeb", async () => {
   expect(Buffer.concat(chunks).toString()).toBe("Hello World!\n");
 });
 
+// fromWeb assigns stream.$bunNativePtr on the node Readable. When user code grafts
+// ReadableStream.prototype into the node stream prototype chain, that put used to
+// reach ReadableStream's private custom setter with the Readable as the receiver,
+// writing a JSValue through a type-confused pointer into the Readable's own
+// property storage (observable below as a clobbered Symbol(kCapture) slot).
+it("Readable.fromWeb with ReadableStream.prototype grafted into the prototype chain", async () => {
+  await using proc = Bun.spawn({
+    cmd: [
+      bunExe(),
+      "-e",
+      `
+        const { Readable } = require("node:stream");
+        const { EventEmitter } = require("node:events");
+        const snap = o => Object.fromEntries(Reflect.ownKeys(o).map(k => [String(k), Object.prototype.toString.call(o[k])]));
+        const before = snap(Readable.fromWeb(new Response("x").body));
+        Object.setPrototypeOf(EventEmitter.prototype, ReadableStream.prototype);
+        const stream = Readable.fromWeb(new Response("y").body);
+        const after = snap(stream);
+        for (const key in before) {
+          if (before[key] !== after[key]) throw new Error("clobbered own slot " + key + ": " + before[key] + " -> " + after[key]);
+        }
+        const chunks = [];
+        for await (const chunk of stream) chunks.push(chunk);
+        console.log("read:" + Buffer.concat(chunks).toString());
+      `,
+    ],
+    env: bunEnv,
+    stderr: "pipe",
+  });
+  const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+  expect(stderr).toBe("");
+  expect(stdout).toBe("read:y\n");
+  expect(exitCode).toBe(0);
+});
+
 // An error from the underlying web stream must surface on the node Readable as an
 // 'error' event (and destroy it), not as a global unhandled rejection.
 it("Readable.fromWeb propagates web stream errors to 'error' and destroys", async () => {