diff --git a/demo/mmap.c b/demo/mmap.c
index e29a122..bc40d18 100644
--- a/demo/mmap.c
+++ b/demo/mmap.c
@@ -110,8 +110,14 @@ int main(int argc, char *argv[])
 		chanlist[i] = CR_PACK(options.channel + i, options.range, options.aref);
 	}
 
-	//prepare_cmd_lib(dev, options.subdevice, options.n_scan, options.n_chan, 1e9 / options.freq, cmd);
-	prepare_cmd(dev, options.subdevice, options.n_scan, options.n_chan, 1e9 / options.freq, cmd);
+	/* prepare_cmd_lib() uses a Comedilib routine to find a
+	 * good command for the device.  prepare_cmd() explicitly
+	 * creates a command, which may not work for your device. */
+	ret = prepare_cmd_lib(dev, options.subdevice, options.n_scan, options.n_chan, 1e9 / options.freq, cmd);
+	//prepare_cmd(dev, options.subdevice, options.n_scan, options.n_chan, 1e9 / options.freq, cmd);
+	if(ret < 0){
+		exit(1);
+	}
 
 	ret = comedi_command_test(dev, cmd);