diff --git a/include/private/surfaceflinger/SharedBufferStack.h b/include/private/surfaceflinger/SharedBufferStack.h
index d689667..d6ae5e9 100644
--- a/include/private/surfaceflinger/SharedBufferStack.h
+++ b/include/private/surfaceflinger/SharedBufferStack.h
@@ -114,8 +114,9 @@
 
     int32_t     identity;       // surface's identity (const)
     int32_t     token;          // surface's token (for debugging)
-    int32_t     reserved32[1];
     Statistics  stats;
+    int8_t      headBuf;        // last retired buffer
+    uint8_t     reservedBytes[3];
     int32_t     reserved;
     BufferData  buffers[NUM_BUFFER_MAX];     // 1024 bytes
 };
@@ -201,6 +202,7 @@
     status_t undoDequeue(int buf);
     
     status_t lock(int buf);
+    status_t cancel(int buf);
     status_t queue(int buf);
     bool needNewBuffer(int buffer) const;
     status_t setDirtyRegion(int buffer, const Region& reg);
@@ -230,8 +232,9 @@
         inline ssize_t operator()();
     };
 
-    struct UndoDequeueUpdate : public UpdateBase {
-        inline UndoDequeueUpdate(SharedBufferBase* sbb);
+    struct CancelUpdate : public UpdateBase {
+        int tail, buf;
+        inline CancelUpdate(SharedBufferBase* sbb, int tail, int buf);
         inline ssize_t operator()();
     };
 
@@ -256,7 +259,6 @@
     int mNumBuffers;
 
     int32_t tail;
-    int32_t undoDequeueTail;
     int32_t queued_head;
     // statistics...
     nsecs_t mDequeueTime[SharedBufferStack::NUM_BUFFER_MAX];
diff --git a/include/surfaceflinger/Surface.h b/include/surfaceflinger/Surface.h
index a210880..cef439c 100644
--- a/include/surfaceflinger/Surface.h
+++ b/include/surfaceflinger/Surface.h
@@ -200,6 +200,7 @@
      */
     static int setSwapInterval(ANativeWindow* window, int interval);
     static int dequeueBuffer(ANativeWindow* window, android_native_buffer_t** buffer);
+    static int cancelBuffer(ANativeWindow* window, android_native_buffer_t* buffer);
     static int lockBuffer(ANativeWindow* window, android_native_buffer_t* buffer);
     static int queueBuffer(ANativeWindow* window, android_native_buffer_t* buffer);
     static int query(ANativeWindow* window, int what, int* value);
@@ -208,6 +209,7 @@
     int dequeueBuffer(android_native_buffer_t** buffer);
     int lockBuffer(android_native_buffer_t* buffer);
     int queueBuffer(android_native_buffer_t* buffer);
+    int cancelBuffer(android_native_buffer_t* buffer);
     int query(int what, int* value);
     int perform(int operation, va_list args);
 
diff --git a/include/ui/egl/android_natives.h b/include/ui/egl/android_natives.h
index d59d72b..654d0f3 100644
--- a/include/ui/egl/android_natives.h
+++ b/include/ui/egl/android_natives.h
@@ -218,7 +218,17 @@
     int     (*perform)(struct ANativeWindow* window,
                 int operation, ... );
     
-    void* reserved_proc[3];
+    /*
+     * hook used to cancel a buffer that has been dequeued.
+     * No synchronization is performed between dequeue() and cancel(), so
+     * either external synchronization is needed, or these functions must be
+     * called from the same thread.
+     */
+    int     (*cancelBuffer)(struct ANativeWindow* window,
+                struct android_native_buffer_t* buffer);
+
+
+    void* reserved_proc[2];
 };
 
 // Backwards compatibility...  please switch to ANativeWindow.
diff --git a/libs/surfaceflinger_client/SharedBufferStack.cpp b/libs/surfaceflinger_client/SharedBufferStack.cpp
index a43b440..8f583f0 100644
--- a/libs/surfaceflinger_client/SharedBufferStack.cpp
+++ b/libs/surfaceflinger_client/SharedBufferStack.cpp
@@ -285,10 +285,12 @@
     return NO_ERROR;
 }
 
-SharedBufferClient::UndoDequeueUpdate::UndoDequeueUpdate(SharedBufferBase* sbb)
-    : UpdateBase(sbb) {    
+SharedBufferClient::CancelUpdate::CancelUpdate(SharedBufferBase* sbb,
+        int tail, int buf)
+    : UpdateBase(sbb), tail(tail), buf(buf) {
 }
-ssize_t SharedBufferClient::UndoDequeueUpdate::operator()() {
+ssize_t SharedBufferClient::CancelUpdate::operator()() {
+    stack.index[tail] = buf;
     android_atomic_inc(&stack.available);
     return NO_ERROR;
 }
@@ -319,7 +321,7 @@
         return BAD_VALUE;
 
     // Preventively lock the current buffer before updating queued.
-    android_atomic_write(stack.index[head], &stack.inUse);
+    android_atomic_write(stack.headBuf, &stack.inUse);
 
     // Decrement the number of queued buffers 
     int32_t queued;
@@ -334,7 +336,9 @@
     // the buffer we preventively locked upon entering this function
 
     head = (head + 1) % numBuffers;
-    android_atomic_write(stack.index[head], &stack.inUse);
+    const int8_t headBuf = stack.index[head];
+    stack.headBuf = headBuf;
+    android_atomic_write(headBuf, &stack.inUse);
 
     // head is only modified here, so we don't need to use cmpxchg
     android_atomic_write(head, &stack.head);
@@ -359,7 +363,7 @@
 SharedBufferClient::SharedBufferClient(SharedClient* sharedClient,
         int surface, int num, int32_t identity)
     : SharedBufferBase(sharedClient, surface, identity),
-      mNumBuffers(num), tail(0), undoDequeueTail(0)
+      mNumBuffers(num), tail(0)
 {
     SharedBufferStack& stack( *mSharedStack );
     tail = computeTail();
@@ -390,7 +394,6 @@
     DequeueUpdate update(this);
     updateCondition( update );
 
-    undoDequeueTail = tail;
     int dequeued = stack.index[tail];
     tail = ((tail+1 >= mNumBuffers) ? 0 : tail+1);
     LOGD_IF(DEBUG_ATOMICS, "dequeued=%d, tail++=%d, %s",
@@ -403,14 +406,19 @@
 
 status_t SharedBufferClient::undoDequeue(int buf)
 {
+    return cancel(buf);
+}
+
+status_t SharedBufferClient::cancel(int buf)
+{
     RWLock::AutoRLock _rd(mLock);
 
-    // TODO: we can only undo the previous dequeue, we should
-    // enforce that in the api
-    UndoDequeueUpdate update(this);
+    // calculate the new position of the tail index (essentially tail--)
+    int localTail = (tail + mNumBuffers - 1) % mNumBuffers;
+    CancelUpdate update(this, localTail, buf);
     status_t err = updateCondition( update );
     if (err == NO_ERROR) {
-        tail = undoDequeueTail;
+        tail = localTail;
     }
     return err;
 }
diff --git a/libs/surfaceflinger_client/Surface.cpp b/libs/surfaceflinger_client/Surface.cpp
index c77d48e..ebb0cc9 100644
--- a/libs/surfaceflinger_client/Surface.cpp
+++ b/libs/surfaceflinger_client/Surface.cpp
@@ -416,6 +416,7 @@
 {
     ANativeWindow::setSwapInterval  = setSwapInterval;
     ANativeWindow::dequeueBuffer    = dequeueBuffer;
+    ANativeWindow::cancelBuffer     = cancelBuffer;
     ANativeWindow::lockBuffer       = lockBuffer;
     ANativeWindow::queueBuffer      = queueBuffer;
     ANativeWindow::query            = query;
@@ -527,6 +528,12 @@
     return self->dequeueBuffer(buffer);
 }
 
+int Surface::cancelBuffer(ANativeWindow* window,
+        android_native_buffer_t* buffer) {
+    Surface* self = getSelf(window);
+    return self->cancelBuffer(buffer);
+}
+
 int Surface::lockBuffer(ANativeWindow* window, 
         android_native_buffer_t* buffer) {
     Surface* self = getSelf(window);
@@ -627,6 +634,33 @@
     return err;
 }
 
+int Surface::cancelBuffer(android_native_buffer_t* buffer)
+{
+    status_t err = validate();
+    switch (err) {
+    case NO_ERROR:
+        // no error, common case
+        break;
+    case INVALID_OPERATION:
+        // legitimate errors here
+        return err;
+    default:
+        // other errors happen because the surface is now invalid,
+        // for instance because it has been destroyed. In this case,
+        // we just fail silently (canceling a buffer is not technically
+        // an error at this point)
+        return NO_ERROR;
+    }
+
+    int32_t bufIdx = getBufferIndex(GraphicBuffer::getSelf(buffer));
+
+    err = mSharedBufferClient->cancel(bufIdx);
+
+    LOGE_IF(err, "error canceling buffer %d (%s)", bufIdx, strerror(-err));
+    return err;
+}
+
+
 int Surface::lockBuffer(android_native_buffer_t* buffer)
 {
     status_t err = validate();
diff --git a/opengl/libagl/egl.cpp b/opengl/libagl/egl.cpp
index 460b74f..239dc05 100644
--- a/opengl/libagl/egl.cpp
+++ b/opengl/libagl/egl.cpp
@@ -1969,7 +1969,7 @@
     if (egl_display_t::is_valid(dpy) == EGL_FALSE)
         return setError(EGL_BAD_DISPLAY, EGL_FALSE);
     // TODO: eglSwapInterval()
-    return setError(EGL_BAD_PARAMETER, EGL_FALSE);
+    return EGL_TRUE;
 }
 
 // ----------------------------------------------------------------------------