diff --git a/src/windows.rs b/src/windows.rs
index 52c6079..3595031 100644
--- a/src/windows.rs
+++ b/src/windows.rs
@@ -59,6 +59,10 @@ pub struct Win32WindowHandle {
 impl Win32WindowHandle {
     /// Create a new handle to a window.
     ///
+    /// # Safety
+    ///
+    /// It is assumed that the Win32 handle belongs to the current thread. This
+    /// is necessary for the handle to be considered "valid" in all cases.
     ///
     /// # Example
     ///