diff --git a/src/lib.rs b/src/lib.rs
index 1e142e3..b813b7f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -188,6 +188,11 @@ pub trait BitFlag: Copy + Clone + 'static + _internal::RawBitFlags {
 pub mod _internal {
     /// A trait automatically implemented by `#[bitflags]` to make the enum
     /// a valid type parameter for `BitFlags<T>`.
+    ///
+    /// # Safety
+    ///
+    /// The values should reflect reality, like they do if the implementation
+    /// is generated by the procmacro.
     pub unsafe trait RawBitFlags: Copy + Clone + 'static {
         /// The underlying integer type.
         type Numeric: BitFlagNum;