diff --git a/libtorrent/src/file.cpp b/libtorrent/src/file.cpp
index 4bbdb8a6..aa62bf22 100644
--- a/libtorrent/src/file.cpp
+++ b/libtorrent/src/file.cpp
@@ -1833,7 +1833,7 @@ typedef struct _FILE_ALLOCATED_RANGE_BUFFER {
 #ifdef FIEMAP_EXTENT_UNKNOWN
 		// for documentation of this feature
 		// http://lwn.net/Articles/297696/
-		struct
+		union
 		{
 			struct fiemap fiemap;
 			struct fiemap_extent extent;