diff --git a/io/iob_send.c b/io/iob_send.c
index 0b89fd9..42f48d7 100644
--- a/io/iob_send.c
+++ b/io/iob_send.c
@@ -51,7 +51,7 @@ int64 iob_send(int64 s,io_batch* b) {
     }
     hdr.headers=v; hdr.hdr_cnt=headers;
     hdr.trailers=v+headers; hdr.trl_cnt=trailers;
-    r=sendfile(e[headers].fd,s,e[headers].offset,e[headers].bytes,&hdr,&sbytes,0);
+    r=sendfile(e[headers].fd,s,e[headers].offset,e[headers].n,&hdr,&sbytes,0);
     if (r==0)
       sent=b->bytesleft;
     else if (r==-1 && errno==EAGAIN)
diff --git a/test/iob.c b/test/iob.c
new file mode 100644
index 0000000..78ddee7
--- /dev/null
+++ b/test/iob.c
@@ -0,0 +1,13 @@
+#include <assert.h>
+#include "iob.h"
+
+main() {
+  int64 fd;
+  io_batch* b;
+  assert(io_readfile(&fd,"GNUmakefile"));
+  assert(b=iob_new(10));
+  assert(iob_addbuf(b,"Huhu",4));
+  assert(iob_addbuf(b," fnord\n",7));
+  assert(iob_addfile(b,fd,10,10));
+  iob_send(1,b);
+}