Index: src/tk/tkbutton.c
--- src/tk/tkbutton.c.orig
+++ src/tk/tkbutton.c
@@ -383,7 +383,7 @@ Tk_ButtonCmd(clientData, interp, argc, argv)
 	    break;
 	default:
 	    sprintf(interp->result,
-		    "unknown button-creation command \"%.50s\"");
+		    "unknown button-creation command \"%.50s\"", argv[0]);
 	    return TCL_ERROR;
     }
 
