diff --git a/include/zephyr.h b/include/zephyr.h
index 0fee5c1f784..8bc08bf34aa 100644
--- a/include/zephyr.h
+++ b/include/zephyr.h
@@ -7,6 +7,14 @@
 #ifndef _ZEPHYR__H
 #define _ZEPHYR__H
 
+/*
+ * Applications can identify whether they are built for Zephyr by
+ * macro below. (It may be already defined by a makefile or toolchain.)
+ */
+#ifndef __ZEPHYR__
+#define __ZEPHYR__
+#endif
+
 #include <kernel.h>
 
 #ifdef CONFIG_MDEF