mmap_span.go | 2 +-

diff --git a/mmap_span.go b/mmap_span.go
index f7d9105923c3125f9eff6cd492a81c7cfd5e5a3e..9d2f39bb31c9c6b1c0d2d42f8020f8dee92ea1dc 100644
--- a/mmap_span.go
+++ b/mmap_span.go
@@ -56,7 +56,7 @@ 		n += _n
 		return len(p) == 0
 	})
 	if len(p) != 0 {
-		err = io.EOF
+		err = io.ErrShortWrite
 	}
 	return
 }