diff --git a/libs/binder/Binder.cpp b/libs/binder/Binder.cpp
index 02321cd..4965386 100644
--- a/libs/binder/Binder.cpp
+++ b/libs/binder/Binder.cpp
@@ -311,15 +311,13 @@
     return NO_ERROR;
 }
 
-void BBinder::attachObject(
-    const void* objectID, void* object, void* cleanupCookie,
-    object_cleanup_func func)
-{
+void* BBinder::attachObject(const void* objectID, void* object, void* cleanupCookie,
+                            object_cleanup_func func) {
     Extras* e = getOrCreateExtras();
-    if (!e) return; // out of memory
+    if (!e) return nullptr; // out of memory
 
     AutoMutex _l(e->mLock);
-    e->mObjects.attach(objectID, object, cleanupCookie, func);
+    return e->mObjects.attach(objectID, object, cleanupCookie, func);
 }
 
 void* BBinder::findObject(const void* objectID) const
@@ -331,13 +329,12 @@
     return e->mObjects.find(objectID);
 }
 
-void BBinder::detachObject(const void* objectID)
-{
+void* BBinder::detachObject(const void* objectID) {
     Extras* e = mExtras.load(std::memory_order_acquire);
-    if (!e) return;
+    if (!e) return nullptr;
 
     AutoMutex _l(e->mLock);
-    e->mObjects.detach(objectID);
+    return e->mObjects.detach(objectID);
 }
 
 BBinder* BBinder::localBinder()
diff --git a/libs/binder/BpBinder.cpp b/libs/binder/BpBinder.cpp
index 5e44a0f..1f67825 100644
--- a/libs/binder/BpBinder.cpp
+++ b/libs/binder/BpBinder.cpp
@@ -61,22 +61,22 @@
     kill();
 }
 
-void BpBinder::ObjectManager::attach(
-    const void* objectID, void* object, void* cleanupCookie,
-    IBinder::object_cleanup_func func)
-{
+void* BpBinder::ObjectManager::attach(const void* objectID, void* object, void* cleanupCookie,
+                                      IBinder::object_cleanup_func func) {
     entry_t e;
     e.object = object;
     e.cleanupCookie = cleanupCookie;
     e.func = func;
 
-    if (mObjects.indexOfKey(objectID) >= 0) {
-        ALOGE("Trying to attach object ID %p to binder ObjectManager %p with object %p, but object ID already in use",
-                objectID, this,  object);
-        return;
+    if (ssize_t idx = mObjects.indexOfKey(objectID); idx >= 0) {
+        ALOGI("Trying to attach object ID %p to binder ObjectManager %p with object %p, but object "
+              "ID already in use",
+              objectID, this, object);
+        return mObjects[idx].object;
     }
 
     mObjects.add(objectID, e);
+    return nullptr;
 }
 
 void* BpBinder::ObjectManager::find(const void* objectID) const
@@ -86,9 +86,12 @@
     return mObjects.valueAt(i).object;
 }
 
-void BpBinder::ObjectManager::detach(const void* objectID)
-{
-    mObjects.removeItem(objectID);
+void* BpBinder::ObjectManager::detach(const void* objectID) {
+    ssize_t idx = mObjects.indexOfKey(objectID);
+    if (idx < 0) return nullptr;
+    void* value = mObjects[idx].object;
+    mObjects.removeItemsAt(idx, 1);
+    return value;
 }
 
 void BpBinder::ObjectManager::kill()
@@ -406,14 +409,11 @@
     recipient->binderDied(wp<BpBinder>::fromExisting(this));
 }
 
-
-void BpBinder::attachObject(
-    const void* objectID, void* object, void* cleanupCookie,
-    object_cleanup_func func)
-{
+void* BpBinder::attachObject(const void* objectID, void* object, void* cleanupCookie,
+                             object_cleanup_func func) {
     AutoMutex _l(mLock);
     ALOGV("Attaching object %p to binder %p (manager=%p)", object, this, &mObjects);
-    mObjects.attach(objectID, object, cleanupCookie, func);
+    return mObjects.attach(objectID, object, cleanupCookie, func);
 }
 
 void* BpBinder::findObject(const void* objectID) const
@@ -422,10 +422,9 @@
     return mObjects.find(objectID);
 }
 
-void BpBinder::detachObject(const void* objectID)
-{
+void* BpBinder::detachObject(const void* objectID) {
     AutoMutex _l(mLock);
-    mObjects.detach(objectID);
+    return mObjects.detach(objectID);
 }
 
 BpBinder* BpBinder::remoteBinder()
diff --git a/libs/binder/include/binder/Binder.h b/libs/binder/include/binder/Binder.h
index 472e546..b2fa250 100644
--- a/libs/binder/include/binder/Binder.h
+++ b/libs/binder/include/binder/Binder.h
@@ -54,12 +54,10 @@
                                         uint32_t flags = 0,
                                         wp<DeathRecipient>* outRecipient = nullptr);
 
-    virtual void        attachObject(   const void* objectID,
-                                        void* object,
-                                        void* cleanupCookie,
-                                        object_cleanup_func func) final;
+    virtual void* attachObject(const void* objectID, void* object, void* cleanupCookie,
+                               object_cleanup_func func) final;
     virtual void*       findObject(const void* objectID) const final;
-    virtual void        detachObject(const void* objectID) final;
+    virtual void* detachObject(const void* objectID) final;
 
     virtual BBinder*    localBinder();
 
diff --git a/libs/binder/include/binder/BpBinder.h b/libs/binder/include/binder/BpBinder.h
index 61bf018..7c89759 100644
--- a/libs/binder/include/binder/BpBinder.h
+++ b/libs/binder/include/binder/BpBinder.h
@@ -72,12 +72,10 @@
                                         uint32_t flags = 0,
                                         wp<DeathRecipient>* outRecipient = nullptr);
 
-    virtual void        attachObject(   const void* objectID,
-                                        void* object,
-                                        void* cleanupCookie,
-                                        object_cleanup_func func) final;
+    virtual void* attachObject(const void* objectID, void* object, void* cleanupCookie,
+                               object_cleanup_func func) final;
     virtual void*       findObject(const void* objectID) const final;
-    virtual void        detachObject(const void* objectID) final;
+    virtual void* detachObject(const void* objectID) final;
 
     virtual BpBinder*   remoteBinder();
 
@@ -91,27 +89,23 @@
     static void         setLimitCallback(binder_proxy_limit_callback cb);
     static void         setBinderProxyCountWatermarks(int high, int low);
 
-    class ObjectManager
-    {
+    class ObjectManager {
     public:
-                    ObjectManager();
-                    ~ObjectManager();
+        ObjectManager();
+        ~ObjectManager();
 
-        void        attach( const void* objectID,
-                            void* object,
-                            void* cleanupCookie,
-                            IBinder::object_cleanup_func func);
-        void*       find(const void* objectID) const;
-        void        detach(const void* objectID);
+        void* attach(const void* objectID, void* object, void* cleanupCookie,
+                     IBinder::object_cleanup_func func);
+        void* find(const void* objectID) const;
+        void* detach(const void* objectID);
 
-        void        kill();
+        void kill();
 
     private:
-                    ObjectManager(const ObjectManager&);
+        ObjectManager(const ObjectManager&);
         ObjectManager& operator=(const ObjectManager&);
 
-        struct entry_t
-        {
+        struct entry_t {
             void* object;
             void* cleanupCookie;
             IBinder::object_cleanup_func func;
diff --git a/libs/binder/include/binder/IBinder.h b/libs/binder/include/binder/IBinder.h
index f9cdac7..4e0952f 100644
--- a/libs/binder/include/binder/IBinder.h
+++ b/libs/binder/include/binder/IBinder.h
@@ -255,26 +255,23 @@
      * objects are invoked with their respective objectID, object, and
      * cleanupCookie. Access to these APIs can be made from multiple threads,
      * but calls from different threads are allowed to be interleaved.
+     *
+     * This returns the object which is already attached. If this returns a
+     * non-null value, it means that attachObject failed. TODO(b/192023359):
+     * remove logs and add [[nodiscard]]
      */
-    virtual void            attachObject(   const void* objectID,
-                                            void* object,
-                                            void* cleanupCookie,
-                                            object_cleanup_func func) = 0;
+    virtual void* attachObject(const void* objectID, void* object, void* cleanupCookie,
+                               object_cleanup_func func) = 0;
     /**
      * Returns object attached with attachObject.
      */
     virtual void*           findObject(const void* objectID) const = 0;
     /**
-     * WARNING: this API does not call the cleanup function for legacy reasons.
-     * It also does not return void* for legacy reasons. If you need to detach
-     * an object and destroy it, there are two options:
-     * - if you can, don't call detachObject and instead wait for the destructor
-     *   to clean it up.
-     * - manually retrieve and destruct the object (if multiple of your threads
-     *   are accessing these APIs, you must guarantee that attachObject isn't
-     *   called after findObject and before detachObject is called).
+     * Returns object attached with attachObject, and detaches it. This does not
+     * delete the object. This is equivalent to using attachObject to attach a null
+     * object.
      */
-    virtual void            detachObject(const void* objectID) = 0;
+    virtual void* detachObject(const void* objectID) = 0;
 
     virtual BBinder*        localBinder();
     virtual BpBinder*       remoteBinder();
diff --git a/libs/binder/tests/Android.bp b/libs/binder/tests/Android.bp
index 8faa3b8..565f88e 100644
--- a/libs/binder/tests/Android.bp
+++ b/libs/binder/tests/Android.bp
@@ -84,7 +84,7 @@
             enabled: false,
         },
     },
-    srcs: ["binderParcelUnitTest.cpp"],
+    srcs: ["binderParcelUnitTest.cpp", "binderBinderUnitTest.cpp"],
     shared_libs: [
         "libbinder",
         "libutils",
diff --git a/libs/binder/tests/binderBinderUnitTest.cpp b/libs/binder/tests/binderBinderUnitTest.cpp
new file mode 100644
index 0000000..1be0c59
--- /dev/null
+++ b/libs/binder/tests/binderBinderUnitTest.cpp
@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <binder/Binder.h>
+#include <binder/IBinder.h>
+#include <gtest/gtest.h>
+
+using android::BBinder;
+using android::OK;
+using android::sp;
+
+const void* kObjectId1 = reinterpret_cast<const void*>(1);
+const void* kObjectId2 = reinterpret_cast<const void*>(2);
+void* kObject1 = reinterpret_cast<void*>(101);
+void* kObject2 = reinterpret_cast<void*>(102);
+void* kObject3 = reinterpret_cast<void*>(103);
+
+TEST(Binder, AttachObject) {
+    auto binder = sp<BBinder>::make();
+    EXPECT_EQ(nullptr, binder->attachObject(kObjectId1, kObject1, nullptr, nullptr));
+    EXPECT_EQ(nullptr, binder->attachObject(kObjectId2, kObject2, nullptr, nullptr));
+    EXPECT_EQ(kObject1, binder->attachObject(kObjectId1, kObject3, nullptr, nullptr));
+}
+
+TEST(Binder, DetachObject) {
+    auto binder = sp<BBinder>::make();
+    EXPECT_EQ(nullptr, binder->attachObject(kObjectId1, kObject1, nullptr, nullptr));
+    EXPECT_EQ(kObject1, binder->detachObject(kObjectId1));
+    EXPECT_EQ(nullptr, binder->attachObject(kObjectId1, kObject2, nullptr, nullptr));
+}