diff --git a/TechnitiumLibrary.Security.OTP/Authenticator.cs b/TechnitiumLibrary.Security.OTP/Authenticator.cs
index a4bdf428..a1f2f3d6 100644
--- a/TechnitiumLibrary.Security.OTP/Authenticator.cs
+++ b/TechnitiumLibrary.Security.OTP/Authenticator.cs
@@ -43,7 +43,7 @@ public class Authenticator
         public Authenticator(AuthenticatorKeyUri keyUri)
         {
             if (!keyUri.Type.Equals("totp", StringComparison.OrdinalIgnoreCase))
-                throw new NotSupportedException($"The authenticator key URI type '{_keyUri.Type}' is not supported.");
+                throw new NotSupportedException($"The authenticator key URI type '{keyUri.Type}' is not supported.");
 
             _keyUri = keyUri;
             _key = Base32.FromBase32String(_keyUri.Secret);