diff --git a/mmtk/Cargo.toml b/mmtk/Cargo.toml
index 3e0f6f63..f405365c 100644
--- a/mmtk/Cargo.toml
+++ b/mmtk/Cargo.toml
@@ -20,7 +20,7 @@ lazy_static = "1.1"
 # - change branch
 # - change repo name
 # But other changes including adding/removing whitespaces in commented lines may break the CI.
-mmtk = { git = "https://github.com/mmtk/mmtk-core.git", rev = "e4d5b4f34578dffa1dad5be537a0e47f80d3ba60" }
+mmtk = { git = "https://github.com/mmtk/mmtk-core.git", rev = "ad824527bc7fa87dfba66cc2cd8745ad1c331b9f" }
 # Uncomment the following to build locally
 # mmtk = { path = "../repos/mmtk-core" }
 
diff --git a/mmtk/rust-toolchain b/mmtk/rust-toolchain
index ca043c6c..adab1484 100644
--- a/mmtk/rust-toolchain
+++ b/mmtk/rust-toolchain
@@ -1 +1 @@
-nightly-2020-12-20
+nightly-2021-05-12
diff --git a/mmtk/src/lib.rs b/mmtk/src/lib.rs
index 6124b0ea..d3ce5f05 100644
--- a/mmtk/src/lib.rs
+++ b/mmtk/src/lib.rs
@@ -1,7 +1,6 @@
 // specialization is considered as an incomplete feature.
 #![allow(incomplete_features)]
 #![feature(specialization)]
-#![feature(const_fn)]
 #![feature(box_syntax)]
 #![feature(vec_into_raw_parts)]
 #![feature(once_cell)]