diff --git a/src/main.ts b/src/main.ts
index c08f015..cda57c8 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -1,7 +1,7 @@
 import * as core from '@actions/core'
-import {boolean} from 'boolean'
+import { boolean } from 'boolean'
 import * as semver from 'semver'
-import {deviceToString, getDevices, simctl} from './xcrun'
+import { deviceToString, getDevices, simctl } from './xcrun'
 
 async function run(): Promise<void> {
   try {
@@ -86,7 +86,11 @@ async function run(): Promise<void> {
 
     core.setOutput('udid', device.udid)
   } catch (error) {
-    core.setFailed(error.message)
+    let errorMessage = 'Failed to run simulator-action (reason unknown)';
+    if (error instanceof Error) {
+      errorMessage = error.message;
+    }
+    core.setFailed(errorMessage);
   }
 }
 
@@ -98,7 +102,11 @@ async function cleanup(): Promise<void> {
       await simctl('shutdown', udid)
     }
   } catch (error) {
-    core.setFailed(error.message)
+    let errorMessage = 'Failed to cleanup simulator-action (reason unknown)';
+    if (error instanceof Error) {
+      errorMessage = error.message;
+    }
+    core.setFailed(errorMessage);
   }
 }