diff --git a/lake-manifest.json b/lake-manifest.json
index e00a7f3..b06c32e 100644
--- a/lake-manifest.json
+++ b/lake-manifest.json
@@ -5,7 +5,7 @@
    "type": "git",
    "subDir": null,
    "scope": "",
-   "rev": "b09d573cbacf5a8e767292e0edeec787a81689ce",
+   "rev": "8668e1ab7c987fb8ed1349f14c3b7b60bd5f27b6",
    "name": "UnicodeBasic",
    "manifestFile": "lake-manifest.json",
    "inputRev": "main",
diff --git a/lean-toolchain b/lean-toolchain
index 5249182..4bafde2 100644
--- a/lean-toolchain
+++ b/lean-toolchain
@@ -1 +1 @@
-leanprover/lean4:v4.27.0
+leanprover/lean4:v4.28.0-rc1