diff --git a/libs/gui/IGraphicBufferProducer.cpp b/libs/gui/IGraphicBufferProducer.cpp
index c3c62358f..51eedab3d 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>
 
@@ -170,8 +171,16 @@ public:
         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 1abb6c375..2e78a6b6f 100644
--- a/libs/gui/Surface.cpp
+++ b/libs/gui/Surface.cpp
@@ -237,6 +237,12 @@ int Surface::dequeueBuffer(android_native_buffer_t** buffer, int* fenceFd) {
         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 bf24ffb7e..1b2f34dfa 100644
--- a/libs/ui/Fence.cpp
+++ b/libs/ui/Fence.cpp
@@ -157,7 +157,7 @@ status_t Fence::unflatten(void const*& buffer, size_t& size, int const*& fds, si
         return INVALID_OPERATION;
     }
 
-    if (size < 1) {
+    if (size < getFlattenedSize()) {
         return NO_MEMORY;
     }