diff --git a/sdk/include/psdk/winuser.h b/sdk/include/psdk/winuser.h
index 07613795e45..ec8249cddf1 100644
--- a/sdk/include/psdk/winuser.h
+++ b/sdk/include/psdk/winuser.h
@@ -836,6 +836,11 @@ extern "C" {
 #define IDTRYAGAIN 10
 #define IDCONTINUE 11
 #endif
+#if (WINVER >= 0x0501)
+#ifndef IDTIMEOUT
+#define IDTIMEOUT 32000
+#endif
+#endif
 
 #define GWL_EXSTYLE (-20)
 #define GWL_STYLE (-16)
diff --git a/sdk/include/psdk/wtsapi32.h b/sdk/include/psdk/wtsapi32.h
index d00a699aacf..d24bff9cfc2 100644
--- a/sdk/include/psdk/wtsapi32.h
+++ b/sdk/include/psdk/wtsapi32.h
@@ -23,6 +23,16 @@
 extern "C" {
 #endif
 
+/*
+ * pResponse values from WTSSendMessage(), in addition
+ * to those from the standard MessageBox() API.
+ */
+#ifndef IDTIMEOUT
+#define IDTIMEOUT 32000
+#endif
+#ifndef IDASYNC
+#define IDASYNC   32001
+#endif
 
 typedef enum _WTS_VIRTUAL_CLASS
 {