diff --git a/tools/testing/selftests/net/tcp_mmap.c b/tools/testing/selftests/net/tcp_mmap.c
index 607cc9ad8d1b..6e59b1461dcc 100644
--- a/tools/testing/selftests/net/tcp_mmap.c
+++ b/tools/testing/selftests/net/tcp_mmap.c
@@ -208,7 +208,7 @@ void *child_thread(void *arg)
 
 			memset(&zc, 0, sizeof(zc));
 			zc.address = (__u64)((unsigned long)addr);
-			zc.length = min(chunk_size, FILE_SZ - lu);
+			zc.length = min(chunk_size, FILE_SZ - total);
 
 			res = getsockopt(fd, IPPROTO_TCP, TCP_ZEROCOPY_RECEIVE,
 					 &zc, &zc_len);