diff --git a/src/window_message.cpp b/src/window_message.cpp
index 8b1d323041b..f8f57596735 100644
--- a/src/window_message.cpp
+++ b/src/window_message.cpp
@@ -590,6 +590,8 @@ void Window_Message::UpdateMessage() {
 				DebugLogText("%d: MSG Sleep \\|");
 				break;
 			default:
+				// Unknown characters will not display anything but do wait.
+				SetWaitForNonPrintable(speed);
 				break;
 			}
 			continue;