diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 090e67a..8c1a7c7 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -28,6 +28,7 @@ jobs:
           cd ../
           git clone https://github.com/leanprover-community/mathlib4
           cd mathlib4
+          lake exe cache get
           lake build
 
       - name: generate docs (PRs only)
diff --git a/lean-toolchain b/lean-toolchain
index a60621d..fc778e0 100644
--- a/lean-toolchain
+++ b/lean-toolchain
@@ -1 +1 @@
-leanprover/lean4:nightly-2022-12-22
+leanprover/lean4:nightly-2023-01-04