diff --git a/src/helper/startup.tcl b/src/helper/startup.tcl
index 6e5f577d7..2f90911ac 100644
--- a/src/helper/startup.tcl
+++ b/src/helper/startup.tcl
@@ -120,7 +120,7 @@ proc unknown {args} {
 		return [eval "$cmd_name [lrange $args 2 end]"]
 	}
 	# This really is an unknown command.
-	puts "Unknown command: $args"
+	return -code error "Unknown command: $args"
 }