diff --git a/CacheObserver/Readme.md b/CacheObserver/Readme.md
index 063ff67..54c04cc 100644
--- a/CacheObserver/Readme.md
+++ b/CacheObserver/Readme.md
@@ -74,3 +74,4 @@ Known good nightly :
 
 - rustc 1.54.0-nightly (eab201df7 2021-06-09)
 - rustc 1.55.0-nightly (885399992 2021-07-06)
+- rustc 1.57.0-nightly (9a28ac83c 2021-09-18)
diff --git a/Readme.md b/Readme.md
index 3a59ddb..ef7d3b1 100644
--- a/Readme.md
+++ b/Readme.md
@@ -20,3 +20,5 @@ Design decision :
 - [ ] Get serial console
 - [ ] Deal with cpuid / floating point niceties
 - [ ] Deal with the user mode switch
+
+Known good rust version : 1.57.0-nightly (9a28ac83c 2021-09-18)