diff --git a/extension/js/common/core/crypto/key.ts b/extension/js/common/core/crypto/key.ts
index 3fd41622eba..07d5478b788 100644
--- a/extension/js/common/core/crypto/key.ts
+++ b/extension/js/common/core/crypto/key.ts
@@ -275,7 +275,8 @@ export class KeyUtil {
       const opgpresult = await OpenPGPKey.diagnose(key, passphrase);
       result = new Map<string, string>([...result, ...opgpresult]);
     }
-    result.set(`expiration`, KeyUtil.formatResult(key.expiration));
+    const expirationIso = key.expiration ? new Date(key.expiration).toISOString() : undefined;
+    result.set(`expiration`, KeyUtil.formatResult(expirationIso));
     result.set(`internal dateBeforeExpiration`, await KeyUtil.formatResultAsync(async () => KeyUtil.dateBeforeExpirationIfAlreadyExpired(key)));
     result.set(`internal usableForEncryption`, KeyUtil.formatResult(key.usableForEncryption));
     result.set(`internal usableForSigning`, KeyUtil.formatResult(key.usableForSigning));
@@ -292,8 +293,9 @@ export class KeyUtil {
     }
   }
 
-  public static formatResult(value: unknown): string {
-    return `[-] ${String(value)}`;
+  public static formatResult(value: unknown | undefined): string {
+    const formattedOutput = value !== undefined ? (value as string) : '-';
+    return `[-] ${formattedOutput}`;
   }
 
   public static async asPublicKey(key: Key): Promise<Key> {
diff --git a/test/source/tests/unit-node.ts b/test/source/tests/unit-node.ts
index 9422d5513b3..1d4577444fb 100644
--- a/test/source/tests/unit-node.ts
+++ b/test/source/tests/unit-node.ts
@@ -1638,8 +1638,8 @@ ZAvn6PBX7vsaReOVa2zsnuY5g70xCxvzHIwR94POu5cENwRtCkrppFnISALpQ1kA
       expect(result.get('SK 0 > SIG 0 > Sig creation time')).to.equal('[-] 1606140328 or 2020-11-23T14:05:28.000Z');
       expect(result.get('SK 0 > SIG 0 > Sig expiration time')).to.equal('[-] -');
       expect(result.get('SK 0 > SIG 0 > Verify')).to.equal('[-] valid');
-      expect(result.get('expiration')).to.equal('[-] undefined');
-      expect(result.get('internal dateBeforeExpiration')).to.equal('[-] undefined');
+      expect(result.get('expiration')).to.equal('[-] -');
+      expect(result.get('internal dateBeforeExpiration')).to.equal('[-] -');
       expect(result.get('internal usableForEncryptionButExpired')).to.equal('[-] false');
       expect(result.get('internal usableForSigningButExpired')).to.equal('[-] false');
       t.pass();
@@ -1676,8 +1676,8 @@ ZAvn6PBX7vsaReOVa2zsnuY5g70xCxvzHIwR94POu5cENwRtCkrppFnISALpQ1kA
       expect(result.get('SK 0 > SIG 0 > Sig creation time')).to.equal('[-] 1606140328 or 2020-11-23T14:05:28.000Z');
       expect(result.get('SK 0 > SIG 0 > Sig expiration time')).to.equal('[-] -');
       expect(result.get('SK 0 > SIG 0 > Verify')).to.equal('[-] valid');
-      expect(result.get('expiration')).to.equal('[-] undefined');
-      expect(result.get('internal dateBeforeExpiration')).to.equal('[-] undefined');
+      expect(result.get('expiration')).to.equal('[-] -');
+      expect(result.get('internal dateBeforeExpiration')).to.equal('[-] -');
       expect(result.get('internal usableForEncryptionButExpired')).to.equal('[-] false');
       expect(result.get('internal usableForSigningButExpired')).to.equal('[-] false');
       t.pass();
@@ -1983,8 +1983,8 @@ jA==
       expect(result.get('SK 0 > SIG 0 > Sig creation time')).to.equal('[-] 1606140328 or 2020-11-23T14:05:28.000Z');
       expect(result.get('SK 0 > SIG 0 > Sig expiration time')).to.equal('[-] -');
       expect(result.get('SK 0 > SIG 0 > Verify')).to.equal('[-] valid');
-      expect(result.get('expiration')).to.equal('[-] undefined');
-      expect(result.get('internal dateBeforeExpiration')).to.equal('[-] undefined');
+      expect(result.get('expiration')).to.equal('[-] -');
+      expect(result.get('internal dateBeforeExpiration')).to.equal('[-] -');
       expect(result.get('internal usableForEncryptionButExpired')).to.equal('[-] false');
       expect(result.get('internal usableForSigningButExpired')).to.equal('[-] false');
       t.pass();
@@ -2022,8 +2022,8 @@ jA==
       expect(result.get('SK 0 > SIG 0 > Sig creation time')).to.equal('[-] 1611140947 or 2021-01-20T11:09:07.000Z');
       expect(result.get('SK 0 > SIG 0 > Sig expiration time')).to.equal('[-] -');
       expect(result.get('SK 0 > SIG 0 > Verify')).to.equal('[-] valid');
-      expect(result.get('expiration')).to.equal('[-] undefined');
-      expect(result.get('internal dateBeforeExpiration')).to.equal('[-] undefined');
+      expect(result.get('expiration')).to.equal('[-] -');
+      expect(result.get('internal dateBeforeExpiration')).to.equal('[-] -');
       expect(result.get('internal usableForEncryptionButExpired')).to.equal('[-] false');
       expect(result.get('internal usableForSigningButExpired')).to.equal('[-] false');
       t.pass();
@@ -2059,8 +2059,8 @@ jA==
       expect(result.get('SK 0 > SIG 0 > Sig creation time')).to.equal('[-] 1611500699 or 2021-01-24T15:04:59.000Z');
       expect(result.get('SK 0 > SIG 0 > Sig expiration time')).to.equal('[-] -');
       expect(result.get('SK 0 > SIG 0 > Verify')).to.equal('[-] valid');
-      expect(result.get('expiration')).to.equal('[-] undefined');
-      expect(result.get('internal dateBeforeExpiration')).to.equal('[-] undefined');
+      expect(result.get('expiration')).to.equal('[-] -');
+      expect(result.get('internal dateBeforeExpiration')).to.equal('[-] -');
       expect(result.get('internal usableForEncryptionButExpired')).to.equal('[-] false');
       expect(result.get('internal usableForSigningButExpired')).to.equal('[-] false');
       t.pass();