diff --git a/.github/workflows/check.yml b/.github/workflows/check.yml
index 21583fad..be4d662d 100644
--- a/.github/workflows/check.yml
+++ b/.github/workflows/check.yml
@@ -45,7 +45,7 @@ jobs:
           NO_ELM_TOOLING_INSTALL: 1
 
       - name: elm-tooling install
-        run: npx --no-install elm-tooling install
+        run: npm run prepare
 
       - name: Flow
         run: npx --no-install flow check
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index bf9c394c..27ba0ff5 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -45,7 +45,7 @@ jobs:
           NO_ELM_TOOLING_INSTALL: 1
 
       - name: elm-tooling install
-        run: npx --no-install elm-tooling install
+        run: npm run prepare
 
       - name: Mocha
         run: npx --no-install mocha tests
diff --git a/elm-tooling-polyfill.js b/elm-tooling-polyfill.js
new file mode 100644
index 00000000..7fd83f42
--- /dev/null
+++ b/elm-tooling-polyfill.js
@@ -0,0 +1,11 @@
+// Only `elm-tooling/getExecutable` supports Node.js 10, the rest of it is
+// Node.js 12+. Luckily, all that’s needed is to polyfill `.flatMap`.
+// We can get rid of this when Node.js 10 becomes EOL 2021-04-30 and support for
+// Node.js 10 is dropped.
+// Note: This is only used during development and CI of node-test-runner, not
+// for users of the npm package.
+if (Array.prototype.flatMap === undefined) {
+  Array.prototype.flatMap = function flatMap(...args) {
+    return [].concat(...this.map(...args));
+  };
+}
diff --git a/package.json b/package.json
index 1ed73bb9..b5e0bd39 100644
--- a/package.json
+++ b/package.json
@@ -16,7 +16,7 @@
     "check": "flow check && npm run lint && npm run format:check && npm run review",
     "format:check": "prettier --check . && elm-format elm --validate",
     "format:write": "prettier --write . && elm-format elm --yes",
-    "prepare": "elm-tooling install"
+    "prepare": "node -r ./elm-tooling-polyfill.js node_modules/elm-tooling/index.js install"
   },
   "repository": {
     "type": "git",