diff --git a/include/private/ui/SharedBufferStack.h b/include/private/ui/SharedBufferStack.h
index 6181f55..8b0f154 100644
--- a/include/private/ui/SharedBufferStack.h
+++ b/include/private/ui/SharedBufferStack.h
@@ -228,6 +228,8 @@
     friend struct Condition;
     friend struct DequeueCondition;
     friend struct LockCondition;
+    
+    int32_t computeTail() const;
 
     struct QueueUpdate : public UpdateBase {
         inline QueueUpdate(SharedBufferBase* sbb);