diff --git a/src/hotplug.rs b/src/hotplug.rs
index 7bdc681..8a8d314 100644
--- a/src/hotplug.rs
+++ b/src/hotplug.rs
@@ -33,3 +33,9 @@ pub enum HotplugEvent {
     /// A device has been disconnected.
     Disconnected(DeviceId),
 }
+
+#[test]
+fn assert_send_sync() {
+    fn require_send_sync<T: Send + Sync>() {}
+    require_send_sync::<HotplugWatch>();
+}
diff --git a/src/platform/macos_iokit/hotplug.rs b/src/platform/macos_iokit/hotplug.rs
index 1b1c88a..175b9be 100644
--- a/src/platform/macos_iokit/hotplug.rs
+++ b/src/platform/macos_iokit/hotplug.rs
@@ -141,6 +141,10 @@ impl MacHotplugWatch {
     }
 }
 
+// Safety: Structurally Send and only method is &mut self, so Sync
+// doesn't have any additional requirements.
+unsafe impl Sync for MacHotplugWatch {}
+
 fn register_notification(
     port: &NotificationPort,
     dictionary: &CFDictionary,
diff --git a/src/platform/windows_winusb/hotplug.rs b/src/platform/windows_winusb/hotplug.rs
index 67cf96b..a151c13 100644
--- a/src/platform/windows_winusb/hotplug.rs
+++ b/src/platform/windows_winusb/hotplug.rs
@@ -115,6 +115,12 @@ impl WindowsHotplugWatch {
     }
 }
 
+// Safety: Effectively a Box<HotplugInner>, which is Send+Sync;
+// `registration` is accessed only in `Drop` and `CM_Unregister_Notification`
+// docs mention using a threadpool to call the function.
+unsafe impl Send for WindowsHotplugWatch {}
+unsafe impl Sync for WindowsHotplugWatch {}
+
 impl Drop for WindowsHotplugWatch {
     fn drop(&mut self) {
         unsafe {