diff --git a/Source/MainWindow.cpp b/Source/MainWindow.cpp
index a96f159..0aa22f9 100644
--- a/Source/MainWindow.cpp
+++ b/Source/MainWindow.cpp
@@ -81,7 +81,7 @@ void MainWindow::closeButtonPressed()
     JUCEApplication::getInstance()->systemRequestedQuit();
 }
 
-BorderSize<int> MainWindow::getBorderThickness()
+BorderSize<int> MainWindow::getBorderThickness() const
 {
     return BorderSize <int>(1);
 }
diff --git a/Source/MainWindow.h b/Source/MainWindow.h
index 2109f7f..e924446 100644
--- a/Source/MainWindow.h
+++ b/Source/MainWindow.h
@@ -39,7 +39,7 @@ class MainWindow : public juce::DocumentWindow
 
     void closeButtonPressed() override;
 
-    juce::BorderSize<int> getBorderThickness() override;
+    juce::BorderSize<int> getBorderThickness() const override;
 
     /* Note: Be careful if you override any DocumentWindow methods - the base
     class uses a lot of them, so by overriding you might break its functionality.