diff --git a/reactos/include/ndk/rtltypes.h b/reactos/include/ndk/rtltypes.h
index 33e640d9800..857174e3b22 100644
--- a/reactos/include/ndk/rtltypes.h
+++ b/reactos/include/ndk/rtltypes.h
@@ -80,6 +80,12 @@ Author:
 #define RTL_CALLER_ALLOCATED_ACTIVATION_CONTEXT_STACK_FRAME_FORMAT_WHISTLER \
                                                             0x1
 
+//
+// RtlActivateActivationContextEx Flags
+//
+#define RTL_ACTIVATE_ACTIVATION_CONTEXT_EX_FLAG_RELEASE_ON_STACK_DEALLOCATION \
+                                                            0x1
+
 //
 // Public Heap Flags
 //