diff --git a/include/uv-private/uv-unix.h b/include/uv-private/uv-unix.h
index a3ef25f2..71253bc9 100644
--- a/include/uv-private/uv-unix.h
+++ b/include/uv-private/uv-unix.h
@@ -78,7 +78,6 @@ typedef void (*uv__io_cb)(struct uv_loop_s* loop, uv__io_t* handle, int events);
 
 struct uv__io_s {
   ev_io io_watcher;
-  uv__io_cb cb;
 };
 
 #define UV_REQ_TYPE_PRIVATE /* empty */
diff --git a/src/unix/core.c b/src/unix/core.c
index bd15c446..49785da0 100644
--- a/src/unix/core.c
+++ b/src/unix/core.c
@@ -594,22 +594,31 @@ uv_err_t uv_chdir(const char* dir) {
 }
 
 
+static void uv__io_set_cb(uv__io_t* handle, uv__io_cb cb) {
+  union { void* data; uv__io_cb cb; } u;
+  u.cb = cb;
+  handle->io_watcher.data = u.data;
+}
+
+
 static void uv__io_rw(struct ev_loop* ev, ev_io* w, int events) {
+  union { void* data; uv__io_cb cb; } u;
   uv_loop_t* loop = ev_userdata(ev);
   uv__io_t* handle = container_of(w, uv__io_t, io_watcher);
-  handle->cb(loop, handle, events & (EV_READ|EV_WRITE|EV_ERROR));
+  u.data = handle->io_watcher.data;
+  u.cb(loop, handle, events & (EV_READ|EV_WRITE|EV_ERROR));
 }
 
 
 void uv__io_init(uv__io_t* handle, uv__io_cb cb, int fd, int events) {
   ev_io_init(&handle->io_watcher, uv__io_rw, fd, events & (EV_READ|EV_WRITE));
-  handle->cb = cb;
+  uv__io_set_cb(handle, cb);
 }
 
 
 void uv__io_set(uv__io_t* handle, uv__io_cb cb, int fd, int events) {
   ev_io_set(&handle->io_watcher, fd, events);
-  handle->cb = cb;
+  uv__io_set_cb(handle, cb);
 }
 
 
diff --git a/src/unix/stream.c b/src/unix/stream.c
index fca57dbb..f441c9b9 100644
--- a/src/unix/stream.c
+++ b/src/unix/stream.c
@@ -918,7 +918,6 @@ int uv_write2(uv_write_t* req, uv_stream_t* stream, uv_buf_t bufs[], int bufcnt,
   ngx_queue_insert_tail(&stream->write_queue, &req->queue);
 
   assert(!ngx_queue_empty(&stream->write_queue));
-  assert(stream->write_watcher.cb == uv__stream_io);
 
   /* If the queue was empty when this function began, we should attempt to
    * do the write immediately. Otherwise start the write_watcher and wait
@@ -976,9 +975,6 @@ int uv__read_start_common(uv_stream_t* stream, uv_alloc_cb alloc_cb,
   stream->read2_cb = read2_cb;
   stream->alloc_cb = alloc_cb;
 
-  /* These should have been set by uv_tcp_init. */
-  assert(stream->read_watcher.cb == uv__stream_io);
-
   uv__io_start(stream->loop, &stream->read_watcher);
   uv__handle_start(stream);