diff --git a/libs/gui/BufferQueueProducer.cpp b/libs/gui/BufferQueueProducer.cpp
index 05923b5..ce47784 100644
--- a/libs/gui/BufferQueueProducer.cpp
+++ b/libs/gui/BufferQueueProducer.cpp
@@ -921,7 +921,11 @@
 
     // Call back without the main BufferQueue lock held, but with the callback
     // lock held so we can ensure that callbacks occur in order
-    {
+
+    int connectedApi;
+    sp<Fence> lastQueuedFence;
+
+    { // scope for the lock
         Mutex::Autolock lock(mCallbackMutex);
         while (callbackTicket != mCurrentCallbackTicket) {
             mCallbackCondition.wait(mCallbackMutex);
@@ -933,20 +937,24 @@
             frameReplacedListener->onFrameReplaced(item);
         }
 
+        connectedApi = mCore->mConnectedApi;
+        lastQueuedFence = std::move(mLastQueueBufferFence);
+
+        mLastQueueBufferFence = std::move(fence);
+        mLastQueuedCrop = item.mCrop;
+        mLastQueuedTransform = item.mTransform;
+
         ++mCurrentCallbackTicket;
         mCallbackCondition.broadcast();
     }
 
     // Wait without lock held
-    if (mCore->mConnectedApi == NATIVE_WINDOW_API_EGL) {
+    if (connectedApi == NATIVE_WINDOW_API_EGL) {
         // Waiting here allows for two full buffers to be queued but not a
         // third. In the event that frames take varying time, this makes a
         // small trade-off in favor of latency rather than throughput.
-        mLastQueueBufferFence->waitForever("Throttling EGL Production");
+        lastQueuedFence->waitForever("Throttling EGL Production");
     }
-    mLastQueueBufferFence = fence;
-    mLastQueuedCrop = item.mCrop;
-    mLastQueuedTransform = item.mTransform;
 
     return NO_ERROR;
 }
diff --git a/libs/gui/IGraphicBufferProducer.cpp b/libs/gui/IGraphicBufferProducer.cpp
index f4ba3bf..1a08130 100644
--- a/libs/gui/IGraphicBufferProducer.cpp
+++ b/libs/gui/IGraphicBufferProducer.cpp
@@ -26,6 +26,7 @@
 #include <binder/Parcel.h>
 #include <binder/IInterface.h>
 
+#include <gui/BufferQueueDefs.h>
 #include <gui/IGraphicBufferProducer.h>
 #include <gui/IProducerListener.h>
 
@@ -203,8 +204,16 @@
         if (result != NO_ERROR) {
             return result;
         }
+
         *slot = reply.readInt32();
         result = reply.readInt32();
+        if (result == NO_ERROR &&
+                (*slot < 0 || *slot >= BufferQueueDefs::NUM_BUFFER_SLOTS)) {
+            ALOGE("attachBuffer returned invalid slot %d", *slot);
+            android_errorWriteLog(0x534e4554, "37478824");
+            return UNKNOWN_ERROR;
+        }
+
         return result;
     }
 
diff --git a/libs/gui/Surface.cpp b/libs/gui/Surface.cpp
index 0838290..5a2ca8d 100644
--- a/libs/gui/Surface.cpp
+++ b/libs/gui/Surface.cpp
@@ -306,6 +306,12 @@
         return result;
     }
 
+    if (buf < 0 || buf >= NUM_BUFFER_SLOTS) {
+        ALOGE("dequeueBuffer: IGraphicBufferProducer returned invalid slot number %d", buf);
+        android_errorWriteLog(0x534e4554, "36991414"); // SafetyNet logging
+        return FAILED_TRANSACTION;
+    }
+
     Mutex::Autolock lock(mMutex);
 
     sp<GraphicBuffer>& gbuf(mSlots[buf].buffer);
diff --git a/libs/ui/Fence.cpp b/libs/ui/Fence.cpp
index bf24ffb..1b2f34d 100644
--- a/libs/ui/Fence.cpp
+++ b/libs/ui/Fence.cpp
@@ -157,7 +157,7 @@
         return INVALID_OPERATION;
     }
 
-    if (size < 1) {
+    if (size < getFlattenedSize()) {
         return NO_MEMORY;
     }