diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index ed1fd5b3..51f2f9f6 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -10,7 +10,7 @@ on:
       - main
       - dev
   schedule:
-    - cron: '0 0 * * *'
+    - cron: "0 0 * * *"
   workflow_dispatch:
 
 defaults:
@@ -23,7 +23,6 @@ jobs:
       fail-fast: false
       matrix:
         os:
-          - ubuntu-18.04
           - ubuntu-20.04
         tool:
           # Note: Specifying the version of valgrind and wasm-pack is not supported.
@@ -32,6 +31,12 @@ jobs:
           # Nextest supports basic version ranges as well
           - nextest@0.9
         include:
+          # Note: mdBook binary is incompatible with ubuntu 18.04,
+          # see https://github.com/rust-lang/mdBook/issues/1779
+          - os: ubuntu-18.04
+            tool: cargo-hack,cargo-llvm-cov,cargo-minimal-versions,parse-changelog,cross,nextest,shellcheck,shfmt,valgrind,wasm-pack,wasmtime
+          - os: ubuntu-18.04
+            tool: cargo-hack@0.5.12,cargo-llvm-cov@0.2.4,cargo-minimal-versions@0.1.3,parse-changelog@0.4.7,cross@0.2.1,nextest@0.9.11,shellcheck@0.8.0,shfmt@3.4.3,wasmtime@0.35.1
           - os: macos-10.15
             tool: cargo-hack,cargo-llvm-cov,cargo-minimal-versions,parse-changelog,cross,nextest,shellcheck,shfmt,wasm-pack,wasmtime,mdbook
           - os: windows-2019