diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 33577c08e7..8b69ccfec2 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -73,14 +73,11 @@ jobs:
     - uses: actions/checkout@v2
       with:
         submodules: true
-    # Note that we use nightly Rust here to get intra-doc links which are a
-    # nightly-only feature right now.
+    # Note that we use nightly Rust for the doc_cfg feature (enabled via `nightlydoc` above)
+    # This version is an older nightly for the new x64 backend (see below)
     - uses: ./.github/actions/install-rust
       with:
-        # TODO (rust-lang/rust#79661): We are seeing an internal compiler error when
-        # building with the latest (2020-12-06) nightly; pin on a slightly older
-        # version for now.
-        toolchain: nightly-2020-11-29
+        toolchain: nightly-2020-12-26
     - run: cargo doc --no-deps --all --exclude wasmtime-cli --exclude test-programs --exclude cranelift-codegen-meta
     - run: cargo doc --package cranelift-codegen-meta --document-private-items
     - uses: actions/upload-artifact@v1
@@ -168,7 +165,7 @@ jobs:
     # flags to rustc.
     - uses: ./.github/actions/install-rust
       with:
-        toolchain: nightly-2020-11-29
+        toolchain: nightly
     - run: cargo install cargo-fuzz --vers "^0.8"
     - run: cargo fetch
       working-directory: ./fuzz
@@ -225,7 +222,7 @@ jobs:
             rust: beta
           - build: nightly
             os: ubuntu-latest
-            rust: nightly-2020-11-29
+            rust: nightly
           - build: macos
             os: macos-latest
             rust: stable
@@ -321,8 +318,10 @@ jobs:
         RUST_BACKTRACE: 1
 
   # Perform all tests (debug mode) for `wasmtime` with the experimental x64
-  # backend. This runs on the nightly channel of Rust (because of issues with
-  # unifying Cargo features on stable) on Ubuntu.
+  # backend. This runs on an older nightly of Rust (because of issues with
+  # unifying Cargo features on stable) on Ubuntu such that it's new enough
+  # to build Wasmtime, but old enough where the -Z options being used
+  # haven't been stabilized yet.
   test_x64:
     name: Test x64 new backend
     runs-on: ubuntu-latest
@@ -332,7 +331,7 @@ jobs:
         submodules: true
     - uses: ./.github/actions/install-rust
       with:
-        toolchain: nightly-2020-11-29
+        toolchain: nightly-2020-12-26
     - uses: ./.github/actions/define-llvm-env
 
     # Install wasm32 targets in order to build various tests throughout the
@@ -343,7 +342,7 @@ jobs:
     # Run the x64 CI script.
     - run: ./ci/run-experimental-x64-ci.sh
       env:
-        CARGO_VERSION: "+nightly-2020-11-29"
+        CARGO_VERSION: "+nightly-2020-12-26"
         RUST_BACKTRACE: 1
 
   # Build and test the wasi-nn module.
@@ -356,7 +355,7 @@ jobs:
           submodules: true
       - uses: ./.github/actions/install-rust
         with:
-          toolchain: nightly-2020-11-29
+          toolchain: nightly
       - run: rustup target add wasm32-wasi
       - uses: ./.github/actions/install-openvino
       - run: ./ci/run-wasi-nn-example.sh