diff --git a/dist/index.js b/dist/index.js
index fb024eb..fbb83c3 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -13667,6 +13667,13 @@ Object.defineProperty(exports, "__esModule", ({ value: true }));
 const core = __importStar(__nccwpck_require__(2186));
 const setup_haskell_1 = __importDefault(__nccwpck_require__(9351));
 const getToggleInput = (name) => core.getInput(name) !== '';
+const getBooleanInput = (name) => {
+    // https://github.com/actions/toolkit/issues/844
+    if (!process.env[`INPUT_${name.replace(/ /g, '_').toUpperCase()}`]) {
+        return undefined;
+    }
+    return core.getBooleanInput(name);
+};
 (0, setup_haskell_1.default)({
     ghcVersion: core.getInput('ghc-version'),
     cabalVersion: core.getInput('cabal-version'),
@@ -13674,7 +13681,7 @@ const getToggleInput = (name) => core.getInput(name) !== '';
     enableStack: getToggleInput('enable-stack'),
     stackNoGlobal: getToggleInput('stack-no-global'),
     stackSetupGhc: getToggleInput('stack-setup-ghc'),
-    cabalUpdate: core.getBooleanInput('cabal-update'),
+    cabalUpdate: getBooleanInput('cabal-update'),
     ghcupReleaseChannels: core.getMultilineInput('ghcup-release-channels'),
     ghcupReleaseChannel: core.getInput('ghcup-release-channel'),
     disableMatcher: getToggleInput('disable-matcher')
diff --git a/src/main.ts b/src/main.ts
index 66b23c0..16a9b56 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -3,6 +3,14 @@ import run from './setup-haskell';
 
 const getToggleInput = (name: string) => core.getInput(name) !== '';
 
+const getBooleanInput = (name: string): boolean | undefined => {
+  // https://github.com/actions/toolkit/issues/844
+  if (!process.env[`INPUT_${name.replace(/ /g, '_').toUpperCase()}`]) {
+    return undefined;
+  }
+  return core.getBooleanInput(name);
+};
+
 run({
   ghcVersion: core.getInput('ghc-version'),
   cabalVersion: core.getInput('cabal-version'),
@@ -10,7 +18,7 @@ run({
   enableStack: getToggleInput('enable-stack'),
   stackNoGlobal: getToggleInput('stack-no-global'),
   stackSetupGhc: getToggleInput('stack-setup-ghc'),
-  cabalUpdate: core.getBooleanInput('cabal-update'),
+  cabalUpdate: getBooleanInput('cabal-update'),
   ghcupReleaseChannels: core.getMultilineInput('ghcup-release-channels'),
   ghcupReleaseChannel: core.getInput('ghcup-release-channel'),
   disableMatcher: getToggleInput('disable-matcher')