diff --git a/src/demoreadersettings.cpp b/src/demoreadersettings.cpp
--- a/src/demoreadersettings.cpp
+++ b/src/demoreadersettings.cpp
@@ -1,5 +1,5 @@
 /*
-  Copyright © 2018 Hasan Yavuz Özderya
+  Copyright © 2019 Hasan Yavuz Özderya
 
   This file is part of serialplot.
 
@@ -21,6 +21,7 @@
 #include "ui_demoreadersettings.h"
 
 #include "utils.h"
+#include "defines.h"
 
 DemoReaderSettings::DemoReaderSettings(QWidget *parent) :
     QWidget(parent),
@@ -28,6 +29,8 @@ DemoReaderSettings::DemoReaderSettings(Q
 {
     ui->setupUi(this);
 
+    ui->spNumChannels->setMaximum(MAX_NUM_CHANNELS);
+
     connect(ui->spNumChannels, SELECT<int>::OVERLOAD_OF(&QSpinBox::valueChanged),
             [this](int value)
             {