diff --git a/include/linux/dio.h b/include/linux/dio.h
index b2dd31c..2cc0fd0 100644
--- a/include/linux/dio.h
+++ b/include/linux/dio.h
@@ -254,7 +254,7 @@
 
 #define dio_resource_start(d) ((d)->resource.start)
 #define dio_resource_end(d)   ((d)->resource.end)
-#define dio_resource_len(d)   ((d)->resource.end-(d)->resource.start+1)
+#define dio_resource_len(d)   (resource_size(&(d)->resource))
 #define dio_resource_flags(d) ((d)->resource.flags)
 
 #define dio_request_device(d, name) \