diff --git a/include/ntfs/support.h b/include/ntfs/support.h
index a9e92cf7..ade65e08 100644
--- a/include/ntfs/support.h
+++ b/include/ntfs/support.h
@@ -46,6 +46,11 @@
 #define max(a,b)	((a) >= (b) ? (a) : (b))
 #endif
 
+/*
+ * Useful macro for determining the offset of a struct member.
+ */
+#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
+
 /*
  * Simple bit operation macros. NOTE: These are NOT atomic.
  */