diff --git a/UsbDk/UsbDkUtil.h b/UsbDk/UsbDkUtil.h
index 2475370..c0cede3 100644
--- a/UsbDk/UsbDkUtil.h
+++ b/UsbDk/UsbDkUtil.h
@@ -3,6 +3,8 @@
 #include <ntddk.h>
 #include <Ntstrsafe.h>
 
+#define ARRAY_SIZE(a) (sizeof(a)/sizeof((a)[0]))
+
 class CWdmSpinLock
 {
 public: