diff -ur a/tclreadline.c b/tclreadline.c
--- a/tclreadline.c	2013-11-16 20:14:28.876272386 +0100
+++ b/tclreadline.c	2013-11-16 20:37:47.455986902 +0100
@@ -234,7 +234,7 @@
 
 	    rl_callback_handler_install(
 			       objc == 3 ? Tcl_GetStringFromObj(objv[2], 0)
-			       : "%", TclReadlineLineCompleteHandler);
+			       : "% ", TclReadlineLineCompleteHandler);
 
 	    Tcl_CreateFileHandler(0, TCL_READABLE,
 		TclReadlineReadHandler, (ClientData) NULL);