diff --git a/src/dns.c b/src/dns.c
index da9b4fdb..fbc8c405 100644
--- a/src/dns.c
+++ b/src/dns.c
@@ -192,7 +192,7 @@ static int luv_getaddrinfo(lua_State* L) {
     return luaL_argerror(L, 4, "callback must be provided");
   }
 #endif
-  req = (uv_getaddrinfo_t*)lua_newuserdata(L, sizeof(*req));
+  req = (uv_getaddrinfo_t*)lua_newuserdata(L, uv_req_size(UV_GETADDRINFO));
   req->data = luv_setup_req(L, ctx, ref);
 
   ret = uv_getaddrinfo(ctx->loop, req, ref == LUA_NOREF ? NULL : luv_getaddrinfo_cb, node, service, hints);
@@ -295,7 +295,7 @@ static int luv_getnameinfo(lua_State* L) {
   }
 #endif
 
-  req = (uv_getnameinfo_t*)lua_newuserdata(L, sizeof(*req));
+  req = (uv_getnameinfo_t*)lua_newuserdata(L, uv_req_size(UV_GETNAMEINFO));
   req->data = luv_setup_req(L, ctx, ref);
 
   ret = uv_getnameinfo(ctx->loop, req, ref == LUA_NOREF ? NULL : luv_getnameinfo_cb, (struct sockaddr*)&addr, flags);
diff --git a/src/fs.c b/src/fs.c
index 321189e9..0c36dccd 100644
--- a/src/fs.c
+++ b/src/fs.c
@@ -459,7 +459,7 @@ static int luv_fs_close(lua_State* L) {
   luv_ctx_t* ctx = luv_context(L);
   uv_file file = luaL_checkinteger(L, 1);
   int ref = luv_check_continuation(L, 2);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(close, req, file);
 }
@@ -470,7 +470,7 @@ static int luv_fs_open(lua_State* L) {
   int flags = luv_check_flags(L, 2);
   int mode = luaL_checkinteger(L, 3);
   int ref = luv_check_continuation(L, 4);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(open, req, path, flags, mode);
 }
@@ -496,7 +496,7 @@ static int luv_fs_read(lua_State* L) {
     return luaL_error(L, "Failure to allocate buffer");
   }
   uv_buf_t buf = uv_buf_init(data, len);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   // TODO: find out why we can't just use req->ptr for the base
   ((luv_req_t*)req->data)->data = buf.base;
@@ -507,7 +507,7 @@ static int luv_fs_unlink(lua_State* L) {
   luv_ctx_t* ctx = luv_context(L);
   const char* path = luaL_checkstring(L, 1);
   int ref = luv_check_continuation(L, 2);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(unlink, req, path);
 }
@@ -526,7 +526,7 @@ static int luv_fs_write(lua_State* L) {
     offset = luaL_optinteger(L, 3, offset);
     ref = luv_check_continuation(L, 4);
   }
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   size_t count;
   uv_buf_t* bufs = luv_check_bufs(L, 2, &count, (luv_req_t*)req->data);
@@ -541,7 +541,7 @@ static int luv_fs_mkdir(lua_State* L) {
   const char* path = luaL_checkstring(L, 1);
   int mode = luaL_checkinteger(L, 2);
   int ref = luv_check_continuation(L, 3);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(mkdir, req, path, mode);
 }
@@ -550,7 +550,7 @@ static int luv_fs_mkdtemp(lua_State* L) {
   luv_ctx_t* ctx = luv_context(L);
   const char* tpl = luaL_checkstring(L, 1);
   int ref = luv_check_continuation(L, 2);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(mkdtemp, req, tpl);
 }
@@ -560,7 +560,7 @@ static int luv_fs_mkstemp(lua_State* L) {
   luv_ctx_t* ctx = luv_context(L);
   const char* tpl = luaL_checkstring(L, 1);
   int ref = luv_check_continuation(L, 2);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(mkstemp, req, tpl);
 }
@@ -570,7 +570,7 @@ static int luv_fs_rmdir(lua_State* L) {
   luv_ctx_t* ctx = luv_context(L);
   const char* path = luaL_checkstring(L, 1);
   int ref = luv_check_continuation(L, 2);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(rmdir, req, path);
 }
@@ -580,7 +580,7 @@ static int luv_fs_scandir(lua_State* L) {
   const char* path = luaL_checkstring(L, 1);
   int flags = 0; // TODO: find out what these flags are.
   int ref = luv_check_continuation(L, 2);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(scandir, req, path, flags);
 }
@@ -603,7 +603,7 @@ static int luv_fs_stat(lua_State* L) {
   luv_ctx_t* ctx = luv_context(L);
   const char* path = luaL_checkstring(L, 1);
   int ref = luv_check_continuation(L, 2);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(stat, req, path);
 }
@@ -612,7 +612,7 @@ static int luv_fs_fstat(lua_State* L) {
   luv_ctx_t* ctx = luv_context(L);
   uv_file file = luaL_checkinteger(L, 1);
   int ref = luv_check_continuation(L, 2);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(fstat, req, file);
 }
@@ -621,7 +621,7 @@ static int luv_fs_lstat(lua_State* L) {
   luv_ctx_t* ctx = luv_context(L);
   const char* path = luaL_checkstring(L, 1);
   int ref = luv_check_continuation(L, 2);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(lstat, req, path);
 }
@@ -631,7 +631,7 @@ static int luv_fs_rename(lua_State* L) {
   const char* path = luaL_checkstring(L, 1);
   const char* new_path = luaL_checkstring(L, 2);
   int ref = luv_check_continuation(L, 3);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   // ref the dest path so that we can print it in the error message
   lua_pushvalue(L, 2);
@@ -643,7 +643,7 @@ static int luv_fs_fsync(lua_State* L) {
   luv_ctx_t* ctx = luv_context(L);
   uv_file file = luaL_checkinteger(L, 1);
   int ref = luv_check_continuation(L, 2);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(fsync, req, file);
 }
@@ -652,7 +652,7 @@ static int luv_fs_fdatasync(lua_State* L) {
   luv_ctx_t* ctx = luv_context(L);
   uv_file file = luaL_checkinteger(L, 1);
   int ref = luv_check_continuation(L, 2);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(fdatasync, req, file);
 }
@@ -662,7 +662,7 @@ static int luv_fs_ftruncate(lua_State* L) {
   uv_file file = luaL_checkinteger(L, 1);
   int64_t offset = luaL_checkinteger(L, 2);
   int ref = luv_check_continuation(L, 3);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(ftruncate, req, file, offset);
 }
@@ -674,7 +674,7 @@ static int luv_fs_sendfile(lua_State* L) {
   int64_t in_offset = luaL_checkinteger(L, 3);
   size_t length = luaL_checkinteger(L, 4);
   int ref = luv_check_continuation(L, 5);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(sendfile, req, out_fd, in_fd, in_offset, length);
 }
@@ -684,7 +684,7 @@ static int luv_fs_access(lua_State* L) {
   const char* path = luaL_checkstring(L, 1);
   int amode = luv_check_amode(L, 2);
   int ref = luv_check_continuation(L, 3);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(access, req, path, amode);
 }
@@ -694,7 +694,7 @@ static int luv_fs_chmod(lua_State* L) {
   const char* path = luaL_checkstring(L, 1);
   int mode = luaL_checkinteger(L, 2);
   int ref = luv_check_continuation(L, 3);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(chmod, req, path, mode);
 }
@@ -704,7 +704,7 @@ static int luv_fs_fchmod(lua_State* L) {
   uv_file file = luaL_checkinteger(L, 1);
   int mode = luaL_checkinteger(L, 2);
   int ref = luv_check_continuation(L, 3);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(fchmod, req, file, mode);
 }
@@ -715,7 +715,7 @@ static int luv_fs_utime(lua_State* L) {
   double atime = luaL_checknumber(L, 2);
   double mtime = luaL_checknumber(L, 3);
   int ref = luv_check_continuation(L, 4);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(utime, req, path, atime, mtime);
 }
@@ -726,7 +726,7 @@ static int luv_fs_futime(lua_State* L) {
   double atime = luaL_checknumber(L, 2);
   double mtime = luaL_checknumber(L, 3);
   int ref = luv_check_continuation(L, 4);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(futime, req, file, atime, mtime);
 }
@@ -738,7 +738,7 @@ static int luv_fs_lutime(lua_State* L) {
   double atime = luaL_checknumber(L, 2);
   double mtime = luaL_checknumber(L, 3);
   int ref = luv_check_continuation(L, 4);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(lutime, req, path, atime, mtime);
 }
@@ -749,7 +749,7 @@ static int luv_fs_link(lua_State* L) {
   const char* path = luaL_checkstring(L, 1);
   const char* new_path = luaL_checkstring(L, 2);
   int ref = luv_check_continuation(L, 3);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   // ref the dest path so that we can print it in the error message
   lua_pushvalue(L, 2);
@@ -783,7 +783,7 @@ static int luv_fs_symlink(lua_State* L) {
     }
     ref = luv_check_continuation(L, 4);
   }
-  req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   // ref the dest path so that we can print it in the error message
   lua_pushvalue(L, 2);
@@ -795,7 +795,7 @@ static int luv_fs_readlink(lua_State* L) {
   luv_ctx_t* ctx = luv_context(L);
   const char* path = luaL_checkstring(L, 1);
   int ref = luv_check_continuation(L, 2);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(readlink, req, path);
 }
@@ -805,7 +805,7 @@ static int luv_fs_realpath(lua_State* L) {
   luv_ctx_t* ctx = luv_context(L);
   const char* path = luaL_checkstring(L, 1);
   int ref = luv_check_continuation(L, 2);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(realpath, req, path);
 }
@@ -817,7 +817,7 @@ static int luv_fs_chown(lua_State* L) {
   uv_uid_t uid = luaL_checkinteger(L, 2);
   uv_uid_t gid = luaL_checkinteger(L, 3);
   int ref = luv_check_continuation(L, 4);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(chown, req, path, uid, gid);
 }
@@ -828,7 +828,7 @@ static int luv_fs_fchown(lua_State* L) {
   uv_uid_t uid = luaL_checkinteger(L, 2);
   uv_uid_t gid = luaL_checkinteger(L, 3);
   int ref = luv_check_continuation(L, 4);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(fchown, req, file, uid, gid);
 }
@@ -840,7 +840,7 @@ static int luv_fs_lchown(lua_State* L) {
   uv_uid_t uid = luaL_checkinteger(L, 2);
   uv_uid_t gid = luaL_checkinteger(L, 3);
   int ref = luv_check_continuation(L, 4);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(lchown, req, path, uid, gid);
 }
@@ -878,7 +878,7 @@ static int luv_fs_copyfile(lua_State*L) {
     }
     ref = luv_check_continuation(L, 4);
   }
-  req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   // ref the dest path so that we can print it in the error message
   lua_pushvalue(L, 2);
@@ -898,7 +898,7 @@ static int luv_fs_opendir(lua_State* L) {
   const char* path = luaL_checkstring(L, 1);
   int ref = luv_check_continuation(L, 2);
   size_t nentries = luaL_optinteger(L, 3, 1);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
 
   //make data_ref to nentries
@@ -914,7 +914,7 @@ static int luv_fs_readdir(lua_State* L) {
   uv_dir_t* dir = luv_check_dir(L, 1);
   int ref = luv_check_continuation(L, 2);
 
-  req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(readdir, req, dir);
 }
@@ -923,7 +923,7 @@ static int luv_fs_closedir(lua_State* L) {
   luv_ctx_t* ctx = luv_context(L);
   uv_dir_t* dir = luv_check_dir(L, 1);
   int ref = luv_check_continuation(L, 2);
-  uv_fs_t *req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t *req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   lua_pushfstring(L, "uv_dir:%p", dir);
   lua_pushnil(L);
@@ -962,7 +962,7 @@ static int luv_fs_statfs(lua_State* L) {
   luv_ctx_t* ctx = luv_context(L);
   const char* path = luaL_checkstring(L, 1);
   int ref = luv_check_continuation(L, 2);
-  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, sizeof(*req));
+  uv_fs_t* req = (uv_fs_t*)lua_newuserdata(L, uv_req_size(UV_FS));
   req->data = luv_setup_req(L, ctx, ref);
   FS_CALL(statfs, req, path);
 }
diff --git a/src/misc.c b/src/misc.c
index d1b06a8a..0bf71d5c 100644
--- a/src/misc.c
+++ b/src/misc.c
@@ -728,7 +728,7 @@ static int luv_random(lua_State* L) {
     // ref buffer
     int buf_ref = luaL_ref(L, LUA_REGISTRYINDEX);
 
-    uv_random_t* req = (uv_random_t*)lua_newuserdata(L, sizeof(*req));
+    uv_random_t* req = (uv_random_t*)lua_newuserdata(L, uv_req_size(UV_RANDOM));
     req->data = luv_setup_req(L, ctx, cb_ref);
     ((luv_req_t*)req->data)->req_ref = buf_ref;
 
diff --git a/src/pipe.c b/src/pipe.c
index 38780ace..aeac40b0 100644
--- a/src/pipe.c
+++ b/src/pipe.c
@@ -56,7 +56,7 @@ static int luv_pipe_connect(lua_State* L) {
   uv_pipe_t* handle = luv_check_pipe(L, 1);
   const char* name = luaL_checkstring(L, 2);
   int ref = luv_check_continuation(L, 3);
-  uv_connect_t* req = (uv_connect_t*)lua_newuserdata(L, sizeof(*req));
+  uv_connect_t* req = (uv_connect_t*)lua_newuserdata(L, uv_req_size(UV_CONNECT));
   req->data = luv_setup_req(L, ctx, ref);
   uv_pipe_connect(req, handle, name, luv_connect_cb);
   return 1;
diff --git a/src/stream.c b/src/stream.c
index 170d9df1..aecd06a5 100644
--- a/src/stream.c
+++ b/src/stream.c
@@ -46,7 +46,7 @@ static int luv_shutdown(lua_State* L) {
   luv_ctx_t* ctx = luv_context(L);
   uv_stream_t* handle = luv_check_stream(L, 1);
   int ref = luv_check_continuation(L, 2);
-  uv_shutdown_t* req = (uv_shutdown_t*)lua_newuserdata(L, sizeof(*req));
+  uv_shutdown_t* req = (uv_shutdown_t*)lua_newuserdata(L, uv_req_size(UV_SHUTDOWN));
   int ret;
   req->data = luv_setup_req(L, ctx, ref);
   ret = uv_shutdown(req, handle, luv_shutdown_cb);
@@ -142,7 +142,7 @@ static int luv_write(lua_State* L) {
   uv_write_t* req;
   int ret, ref;
   ref = luv_check_continuation(L, 3);
-  req = (uv_write_t *)lua_newuserdata(L, sizeof(*req));
+  req = (uv_write_t *)lua_newuserdata(L, uv_req_size(UV_WRITE));
   req->data = (luv_req_t*)luv_setup_req(L, ctx, ref);
   size_t count;
   uv_buf_t* bufs = luv_check_bufs(L, 2, &count, (luv_req_t*)req->data);
@@ -164,7 +164,7 @@ static int luv_write2(lua_State* L) {
   uv_stream_t* send_handle;
   send_handle = luv_check_stream(L, 3);
   ref = luv_check_continuation(L, 4);
-  req = (uv_write_t *)lua_newuserdata(L, sizeof(*req));
+  req = (uv_write_t *)lua_newuserdata(L, uv_req_size(UV_WRITE));
   req->data = luv_setup_req(L, ctx, ref);
   size_t count;
   uv_buf_t* bufs = luv_check_bufs(L, 2, &count, (luv_req_t*)req->data);
diff --git a/src/tcp.c b/src/tcp.c
index a6bb95d9..c346b7f1 100644
--- a/src/tcp.c
+++ b/src/tcp.c
@@ -190,7 +190,7 @@ static int luv_tcp_connect(lua_State* L) {
   }
   ref = luv_check_continuation(L, 4);
 
-  req = (uv_connect_t*)lua_newuserdata(L, sizeof(*req));
+  req = (uv_connect_t*)lua_newuserdata(L, uv_req_size(UV_CONNECT));
   req->data = luv_setup_req(L, lhandle->ctx, ref);
   ret = uv_tcp_connect(req, handle, (struct sockaddr*)&addr, luv_connect_cb);
   if (ret < 0) {
diff --git a/src/udp.c b/src/udp.c
index d017a0e0..d13372ff 100644
--- a/src/udp.c
+++ b/src/udp.c
@@ -294,7 +294,7 @@ static int luv_udp_send(lua_State* L) {
   luv_handle_t* lhandle = handle->data;
   addr_ptr = luv_check_addr(L, &addr, 3, 4);
   ref = luv_check_continuation(L, 5);
-  req = (uv_udp_send_t*)lua_newuserdata(L, sizeof(*req));
+  req = (uv_udp_send_t*)lua_newuserdata(L, uv_req_size(UV_UDP_SEND));
   req->data = luv_setup_req(L, lhandle->ctx, ref);
   size_t count;
   uv_buf_t* bufs = luv_check_bufs(L, 2, &count, (luv_req_t*)req->data);