diff --git a/libs/binder/ndk/ibinder.cpp b/libs/binder/ndk/ibinder.cpp
index 28d1f16..d0de7b9 100644
--- a/libs/binder/ndk/ibinder.cpp
+++ b/libs/binder/ndk/ibinder.cpp
@@ -75,12 +75,48 @@
 AIBinder::AIBinder(const AIBinder_Class* clazz) : mClazz(clazz) {}
 AIBinder::~AIBinder() {}
 
-std::optional<bool> AIBinder::associateClassInternal(const AIBinder_Class* clazz,
-                                                     const String16& newDescriptor, bool set) {
+// b/175635923 libcxx causes "implicit-conversion" with a string with invalid char
+static std::string SanitizeString(const String16& str) {
+    std::string sanitized{String8(str)};
+    for (auto& c : sanitized) {
+        if (!isprint(c)) {
+            c = '?';
+        }
+    }
+    return sanitized;
+}
+
+bool AIBinder::associateClass(const AIBinder_Class* clazz) {
+    if (clazz == nullptr) return false;
+
+    // If mClazz is non-null, this must have been called and cached
+    // already. So, we can safely call this first. Due to the implementation
+    // of getInterfaceDescriptor (at time of writing), two simultaneous calls
+    // may lead to extra binder transactions, but this is expected to be
+    // exceedingly rare. Once we have a binder, when we get it again later,
+    // we won't make another binder transaction here.
+    const String16& descriptor = getBinder()->getInterfaceDescriptor();
+    const String16& newDescriptor = clazz->getInterfaceDescriptor();
+
     std::lock_guard<std::mutex> lock(mClazzMutex);
     if (mClazz == clazz) return true;
 
-    if (mClazz != nullptr) {
+    // If this is an ABpBinder, the first class object becomes the canonical one. The implication
+    // of this is that no API can require a proxy information to get information on how to behave.
+    // from the class itself - which should only store the interface descriptor. The functionality
+    // should be implemented by adding AIBinder_* APIs to set values on binders themselves, by
+    // setting things on AIBinder_Class which get transferred along with the binder, so that they
+    // can be read along with the BpBinder, or by modifying APIs directly (e.g. an option in
+    // onTransact).
+    //
+    // While this check is required to support linkernamespaces, one downside of it is that
+    // you may parcel code to communicate between things in the same process. However, comms
+    // between linkernamespaces like this already happen for cross-language calls like Java<->C++
+    // or Rust<->Java, and there are good stability guarantees here. This interacts with
+    // binder Stability checks exactly like any other in-process call. The stability is known
+    // to the IBinder object, so that it doesn't matter if a class object comes from
+    // a different stability level.
+    if (mClazz != nullptr && !asABpBinder()) {
         const String16& currentDescriptor = mClazz->getInterfaceDescriptor();
         if (newDescriptor == currentDescriptor) {
             LOG(ERROR) << __func__ << ": Class descriptors '" << currentDescriptor
@@ -97,37 +133,10 @@
         return false;
     }
 
-    if (set) {
-        // if this is a local object, it's not one known to libbinder_ndk
-        mClazz = clazz;
-        return true;
-    }
-
-    return {};
-}
-
-// b/175635923 libcxx causes "implicit-conversion" with a string with invalid char
-static std::string SanitizeString(const String16& str) {
-    std::string sanitized{String8(str)};
-    for (auto& c : sanitized) {
-        if (!isprint(c)) {
-            c = '?';
-        }
-    }
-    return sanitized;
-}
-
-bool AIBinder::associateClass(const AIBinder_Class* clazz) {
-    if (clazz == nullptr) return false;
-
-    const String16& newDescriptor = clazz->getInterfaceDescriptor();
-
-    auto result = associateClassInternal(clazz, newDescriptor, false);
-    if (result.has_value()) return *result;
-
-    CHECK(asABpBinder() != nullptr);  // ABBinder always has a descriptor
-
-    const String16& descriptor = getBinder()->getInterfaceDescriptor();
+    // This will always be an O(n) comparison, but it's expected to be extremely rare.
+    // since it's an error condition. Do the comparison after we take the lock and
+    // check the pointer equality fast path. By always taking the lock, it's also
+    // more flake-proof. However, the check is not dependent on the lock.
     if (descriptor != newDescriptor) {
         if (getBinder()->isBinderAlive()) {
             LOG(ERROR) << __func__ << ": Expecting binder to have class '" << newDescriptor
@@ -141,7 +150,14 @@
         return false;
     }
 
-    return associateClassInternal(clazz, newDescriptor, true).value();
+    // A local binder being set for the first time OR
+    // ignoring a proxy binder which is set multiple time, by considering the first
+    // associated class as the canonical one.
+    if (mClazz == nullptr) {
+        mClazz = clazz;
+    }
+
+    return true;
 }
 
 ABBinder::ABBinder(const AIBinder_Class* clazz, void* userData)
@@ -325,6 +341,10 @@
     return lhs->binder < rhs->binder;
 }
 
+// WARNING: When multiple classes exist with the same interface descriptor in different
+// linkernamespaces, the first one to be associated with mClazz becomes the canonical one
+// and the only requirement on this is that the interface descriptors match. If this
+// is an ABpBinder, no other state can be referenced from mClazz.
 AIBinder_Class::AIBinder_Class(const char* interfaceDescriptor, AIBinder_Class_onCreate onCreate,
                                AIBinder_Class_onDestroy onDestroy,
                                AIBinder_Class_onTransact onTransact)
@@ -632,6 +652,10 @@
     (*in)->get()->markForBinder(binder->getBinder());
 
     status_t status = android::OK;
+
+    // note - this is the only read of a value in clazz, and it comes with a warning
+    // on the API itself. Do not copy this design. Instead, attach data in a new
+    // version of the prepareTransaction function.
     if (clazz->writeHeader) {
         status = (*in)->get()->writeInterfaceToken(clazz->getInterfaceDescriptor());
     }
diff --git a/libs/binder/ndk/ibinder_internal.h b/libs/binder/ndk/ibinder_internal.h
index d7098e8..67bb092 100644
--- a/libs/binder/ndk/ibinder_internal.h
+++ b/libs/binder/ndk/ibinder_internal.h
@@ -53,12 +53,14 @@
     }
 
    private:
-    std::optional<bool> associateClassInternal(const AIBinder_Class* clazz,
-                                               const ::android::String16& newDescriptor, bool set);
-
     // AIBinder instance is instance of this class for a local object. In order to transact on a
     // remote object, this also must be set for simplicity (although right now, only the
     // interfaceDescriptor from it is used).
+    //
+    // WARNING: When multiple classes exist with the same interface descriptor in different
+    // linkernamespaces, the first one to be associated with mClazz becomes the canonical one
+    // and the only requirement on this is that the interface descriptors match. If this
+    // is an ABpBinder, no other state can be referenced from mClazz.
     const AIBinder_Class* mClazz;
     std::mutex mClazzMutex;
 };
diff --git a/libs/binder/ndk/include_ndk/android/binder_ibinder.h b/libs/binder/ndk/include_ndk/android/binder_ibinder.h
index 1af2119..05677a8 100644
--- a/libs/binder/ndk/include_ndk/android/binder_ibinder.h
+++ b/libs/binder/ndk/include_ndk/android/binder_ibinder.h
@@ -229,6 +229,11 @@
  *
  * Available since API level 33.
  *
+ * WARNING: this API interacts badly with linkernamespaces. For correct behavior, you must
+ * use it on all instances of a class in the same process which share the same interface
+ * descriptor. In general, it is recommended you do not use this API, because it is disabling
+ * type safety.
+ *
  * \param clazz class to disable interface header on.
  */
 void AIBinder_Class_disableInterfaceTokenHeader(AIBinder_Class* clazz) __INTRODUCED_IN(33);
diff --git a/libs/binder/ndk/tests/iface.cpp b/libs/binder/ndk/tests/iface.cpp
index 2afe5d2..76acff5 100644
--- a/libs/binder/ndk/tests/iface.cpp
+++ b/libs/binder/ndk/tests/iface.cpp
@@ -72,6 +72,11 @@
 AIBinder_Class* IFoo::kClass = AIBinder_Class_define(kIFooDescriptor, IFoo_Class_onCreate,
                                                      IFoo_Class_onDestroy, IFoo_Class_onTransact);
 
+// Defines the same class. Ordinarly, you would never want to do this, but it's done here
+// to simulate what would happen when multiple linker namespaces interact.
+AIBinder_Class* IFoo::kClassDupe = AIBinder_Class_define(
+        kIFooDescriptor, IFoo_Class_onCreate, IFoo_Class_onDestroy, IFoo_Class_onTransact);
+
 class BpFoo : public IFoo {
    public:
     explicit BpFoo(AIBinder* binder) : mBinder(binder) {}
diff --git a/libs/binder/ndk/tests/include/iface/iface.h b/libs/binder/ndk/tests/include/iface/iface.h
index 7408d0c..0a562f0 100644
--- a/libs/binder/ndk/tests/include/iface/iface.h
+++ b/libs/binder/ndk/tests/include/iface/iface.h
@@ -30,8 +30,13 @@
     static const char* kIFooDescriptor;
 
     static AIBinder_Class* kClass;
+    static AIBinder_Class* kClassDupe;
 
     // binder representing this interface with one reference count
+    // NOTE - this will create a new binder if it already exists. If you use
+    // getService for instance, you must pull outBinder. Don't use this without
+    // verifying isRemote or pointer equality. This is not a very good testing API - don't
+    // copy it - consider the AIDL-generated APIs instead.
     AIBinder* getBinder();
 
     // Takes ownership of IFoo
diff --git a/libs/binder/ndk/tests/libbinder_ndk_unit_test.cpp b/libs/binder/ndk/tests/libbinder_ndk_unit_test.cpp
index 9d5ef68..5b2532a 100644
--- a/libs/binder/ndk/tests/libbinder_ndk_unit_test.cpp
+++ b/libs/binder/ndk/tests/libbinder_ndk_unit_test.cpp
@@ -55,6 +55,18 @@
 constexpr unsigned int kShutdownWaitTime = 10;
 constexpr uint64_t kContextTestValue = 0xb4e42fb4d9a1d715;
 
+class MyTestFoo : public IFoo {
+    binder_status_t doubleNumber(int32_t in, int32_t* out) override {
+        *out = 2 * in;
+        LOG(INFO) << "doubleNumber (" << in << ") => " << *out;
+        return STATUS_OK;
+    }
+    binder_status_t die() override {
+        ADD_FAILURE() << "die called on local instance";
+        return STATUS_OK;
+    }
+};
+
 class MyBinderNdkUnitTest : public aidl::BnBinderNdkUnitTest {
     ndk::ScopedAStatus repeatInt(int32_t in, int32_t* out) {
         *out = in;
@@ -296,11 +308,10 @@
 }
 
 TEST(NdkBinder, UnimplementedDump) {
-    sp<IFoo> foo = IFoo::getService(IFoo::kSomeInstanceName);
+    ndk::SpAIBinder binder;
+    sp<IFoo> foo = IFoo::getService(IFoo::kSomeInstanceName, binder.getR());
     ASSERT_NE(foo, nullptr);
-    AIBinder* binder = foo->getBinder();
-    EXPECT_EQ(OK, AIBinder_dump(binder, STDOUT_FILENO, nullptr, 0));
-    AIBinder_decStrong(binder);
+    EXPECT_EQ(OK, AIBinder_dump(binder.get(), STDOUT_FILENO, nullptr, 0));
 }
 
 TEST(NdkBinder, UnimplementedShell) {
@@ -324,6 +335,24 @@
     EXPECT_EQ(2, out);
 }
 
+TEST(NdkBinder, ReassociateBpBinderWithSameDescriptor) {
+    ndk::SpAIBinder binder;
+    sp<IFoo> foo = IFoo::getService(IFoo::kSomeInstanceName, binder.getR());
+
+    EXPECT_TRUE(AIBinder_isRemote(binder.get()));
+
+    EXPECT_TRUE(AIBinder_associateClass(binder.get(), IFoo::kClassDupe));
+}
+
+TEST(NdkBinder, CantHaveTwoLocalBinderClassesWithSameDescriptor) {
+    sp<IFoo> foo = sp<MyTestFoo>::make();
+    ndk::SpAIBinder binder(foo->getBinder());
+
+    EXPECT_FALSE(AIBinder_isRemote(binder.get()));
+
+    EXPECT_FALSE(AIBinder_associateClass(binder.get(), IFoo::kClassDupe));
+}
+
 TEST(NdkBinder, GetTestServiceStressTest) {
     // libbinder has some complicated logic to make sure only one instance of
     // ABpBinder is associated with each binder.
@@ -545,18 +574,6 @@
     AIBinder_decStrong(binder);
 }
 
-class MyTestFoo : public IFoo {
-    binder_status_t doubleNumber(int32_t in, int32_t* out) override {
-        *out = 2 * in;
-        LOG(INFO) << "doubleNumber (" << in << ") => " << *out;
-        return STATUS_OK;
-    }
-    binder_status_t die() override {
-        ADD_FAILURE() << "die called on local instance";
-        return STATUS_OK;
-    }
-};
-
 TEST(NdkBinder, SetInheritRt) {
     // functional test in binderLibTest
     sp<IFoo> foo = sp<MyTestFoo>::make();
@@ -597,7 +614,8 @@
     sp<IFoo> foo = new MyTestFoo;
     EXPECT_EQ(EX_NONE, foo->addService(kInstanceName));
 
-    sp<IFoo> getFoo = IFoo::getService(kInstanceName);
+    ndk::SpAIBinder binder;
+    sp<IFoo> getFoo = IFoo::getService(kInstanceName, binder.getR());
     EXPECT_EQ(foo.get(), getFoo.get());
 
     int32_t out;