diff --git a/reactos/include/ndk/amd64/ketypes.h b/reactos/include/ndk/amd64/ketypes.h
index fb97dbc7339..9e9042fa19a 100644
--- a/reactos/include/ndk/amd64/ketypes.h
+++ b/reactos/include/ndk/amd64/ketypes.h
@@ -253,7 +253,10 @@ typedef struct _KCALLOUT_FRAME
 //
 // Dummy LDT_ENTRY
 //
+#ifndef _LDT_ENTRY_DEFINED
+#define _LDT_ENTRY_DEFINED
 typedef ULONG LDT_ENTRY;
+#endif
 
 //
 // GDT Entry Definition