diff --git a/src/unix/fs.c b/src/unix/fs.c
index 626d6c05..2f4ab871 100644
--- a/src/unix/fs.c
+++ b/src/unix/fs.c
@@ -1476,6 +1476,9 @@ int uv_fs_copyfile(uv_loop_t* loop,
                    const char* new_path,
                    int flags,
                    uv_fs_cb cb) {
+  if (flags & ~UV_FS_COPYFILE_EXCL)
+    return -EINVAL;
+
   INIT(COPYFILE);
   PATH2;
   req->flags = flags;
diff --git a/src/win/fs.c b/src/win/fs.c
index 9ef29fea..5edfee88 100644
--- a/src/win/fs.c
+++ b/src/win/fs.c
@@ -2434,6 +2434,9 @@ int uv_fs_copyfile(uv_loop_t* loop,
                    uv_fs_cb cb) {
   int err;
 
+  if (flags & ~UV_FS_COPYFILE_EXCL)
+    return UV_EINVAL;
+
   uv_fs_req_init(loop, req, UV_FS_COPYFILE, cb);
   err = fs__capture_path(req, path, new_path, cb != NULL);
 
diff --git a/test/test-fs-copyfile.c b/test/test-fs-copyfile.c
index 746cd94b..a973e86a 100644
--- a/test/test-fs-copyfile.c
+++ b/test/test-fs-copyfile.c
@@ -96,6 +96,10 @@ TEST_IMPL(fs_copyfile) {
 
   loop = uv_default_loop();
 
+  /* Fails with EINVAL if bad flags are passed. */
+  r = uv_fs_copyfile(NULL, &req, src, dst, -1, NULL);
+  ASSERT(r == UV_EINVAL);
+
   /* Fails with ENOENT if source does not exist. */
   unlink(src);
   unlink(dst);