diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 06379cc87f59..9f29ed743425 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -1822,17 +1822,19 @@ fetch_mmaped_event(struct perf_session *session,
 
 struct reader {
 	int	fd;
+	u64	data_size;
 };
 
 static int __perf_session__process_events(struct perf_session *session)
 {
 	struct reader rd = {
 		.fd		= perf_data__fd(session->data),
+		.data_size	= session->header.data_size,
 	};
 	struct ordered_events *oe = &session->ordered_events;
 	struct perf_tool *tool = session->tool;
 	u64 data_offset = session->header.data_offset;
-	u64 data_size = session->header.data_size;
+	u64 data_size = rd.data_size;
 	u64 head, page_offset, file_offset, file_pos, size;
 	int err, mmap_prot, mmap_flags, map_idx = 0;
 	size_t	mmap_size;