diff --git a/reactos/lib/rtl/rtl.h b/reactos/lib/rtl/rtl.h
index e2609bca6f8..336cdf73292 100644
--- a/reactos/lib/rtl/rtl.h
+++ b/reactos/lib/rtl/rtl.h
@@ -8,6 +8,9 @@
 
 /* INCLUDES ******************************************************************/
 
+#ifndef RTL_H
+#define RTL_H
+
 /* We're a core NT DLL, we don't import syscalls */
 #define WIN32_NO_STATUS
 #define _INC_SWPRINTF_INL_
@@ -25,4 +28,6 @@
 
 #include <pseh/pseh.h>
 
+#endif /* RTL_H */
+
 /* EOF */