diff --git a/reactos/subsys/win32k/ntuser/csr.c b/reactos/subsys/win32k/ntuser/csr.c
index 6cb06c98e00..1ebec16e458 100644
--- a/reactos/subsys/win32k/ntuser/csr.c
+++ b/reactos/subsys/win32k/ntuser/csr.c
@@ -54,8 +54,8 @@ CsrNotify(PCSR_API_MESSAGE Request)
       return STATUS_INVALID_PORT_HANDLE;
     }
 
-  Request->Header.DataSize = sizeof(CSR_API_MESSAGE) - LPC_MESSAGE_BASE_SIZE;
-  Request->Header.MessageSize = sizeof(CSR_API_MESSAGE);
+  Request->Header.u1.s1.DataLength = sizeof(CSR_API_MESSAGE) - LPC_MESSAGE_BASE_SIZE;
+  Request->Header.u1.s1.TotalLength = sizeof(CSR_API_MESSAGE);
 
   /* Switch to the process in which the WindowsApiPort handle is valid */
   OldProcess = PsGetCurrentProcess();