diff --git a/Lib-rand.md b/Lib-rand.md
index 476acde..210353e 100644
--- a/Lib-rand.md
+++ b/Lib-rand.md
@@ -112,6 +112,6 @@ Very common/important:
 
 ### Additional implementation notes
 
-  - _note_
+  - `Rng` should take `&mut self`, instead of forcing the use of mutable fields
   - _note_
   - _note_
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