diff --git a/RhinoReminds/Program.cs b/RhinoReminds/Program.cs
index 9745541..a3ae593 100644
--- a/RhinoReminds/Program.cs
+++ b/RhinoReminds/Program.cs
@@ -74,6 +74,10 @@ namespace RhinoReminds
 					case "--pidfile":
 						settings.PidFile = args[++i];
 						break;
+
+					default:
+						Console.Error.WriteLine($"Error: Unknown argument '{args[i]}'.");
+						return 14;
 				}
 			}