diff --git a/include/wtypes.idl b/include/wtypes.idl
index 0e0fed7c773..49aadbcbda6 100644
--- a/include/wtypes.idl
+++ b/include/wtypes.idl
@@ -135,7 +135,7 @@ typedef struct _SECURITY_DESCRIPTOR {
 typedef struct _SECURITY_ATTRIBUTES
 {
     DWORD nLength;
-    LPVOID lpSecurityDescriptor;
+    [size_is(nLength)] LPVOID lpSecurityDescriptor;
     BOOL bInheritHandle;
 } SECURITY_ATTRIBUTES, *PSECURITY_ATTRIBUTES, *LPSECURITY_ATTRIBUTES;