diff --git a/src/xbus/messages.cpp b/src/xbus/messages.cpp
index 6164ec521..a8efc78b6 100644
--- a/src/xbus/messages.cpp
+++ b/src/xbus/messages.cpp
@@ -19,13 +19,6 @@
 namespace XBus
 {
 
-
-    const int c_screenWidth = 1024;
-    const int c_screenHeight = 768;
-    const int c_boxLeft = 128;
-    const int c_boxTop = c_screenHeight - 16;
-    const int c_boxRight = c_screenWidth - 128;
-
     void CMessageBox::draw()
     {
         const int messageCount = static_cast<int>(m_messages.size());
@@ -75,7 +68,8 @@ namespace XBus
         return len;
     }
 
-    CMessageBoxControl::CMessageBoxControl() :
+    CMessageBoxControl::CMessageBoxControl(int left, int right, int top) :
+        m_messageBox(left, right, top),
         m_showCommand("org/swift-project/xbus/show_messages", "Show XBus text messages", [this] { show(); }),
         m_hideCommand("org/swift-project/xbus/hide_messages", "Hide XBus text messages", [this] { hide(); }),
         m_toggleCommand("org/swift-project/xbus/toggle_messages", "Toggle XBus text messages", [this] { toggle(); }),
diff --git a/src/xbus/messages.h b/src/xbus/messages.h
index 0a86b5bb4..149d7e65f 100644
--- a/src/xbus/messages.h
+++ b/src/xbus/messages.h
@@ -28,7 +28,7 @@ namespace XBus
     struct CMessage
     {
         //! Constructor.
-        CMessage(const std::string &text, float r, float g, float b) : m_text(text), m_rgb{{ r, g, b }} {}
+        CMessage(const std::string &text, float r = 1, float g = 1, float b = 1) : m_text(text), m_rgb{{ r, g, b }} {}
 
         //! Text.
         std::string m_text;
@@ -44,7 +44,11 @@ namespace XBus
     {
     public:
         //! Constructor.
-        CMessageBox() : CDrawable(xplm_Phase_Window, true) {}
+        //! \param left Number of "virtual pixels" between screen left edge and box left edge.
+        //! \param right Number of "virtual pixels" between screen right edge and box right edge.
+        //! \param top Number of "virtual pixels" between screen top edge and box top edge.
+        CMessageBox(int left, int right, int top) : CDrawable(xplm_Phase_Window, true),
+            c_boxLeft(left), c_boxRight(c_screenWidth - right), c_boxTop(c_screenHeight - top) {}
 
         //! Set messages to draw in message box, from a pair of iterators.
         template <typename Iterator>
@@ -71,6 +75,11 @@ namespace XBus
         std::vector<CMessage> m_messages;
         bool m_upArrow = false;
         bool m_downArrow = false;
+        const int c_boxLeft = 0;
+        const int c_boxRight = 0;
+        const int c_boxTop = 0;
+        constexpr static int c_screenWidth = 1024;
+        constexpr static int c_screenHeight = 768;
     };
 
     /*!
@@ -79,8 +88,8 @@ namespace XBus
     class CMessageBoxControl
     {
     public:
-        //! Constructor.
-        CMessageBoxControl();
+        //! \copydoc CMessageBox::CMessageBox
+        CMessageBoxControl(int left, int right, int top);
 
         //! Add a new message to the bottom of the list.
         void addMessage(const CMessage &message);
diff --git a/src/xbus/service.h b/src/xbus/service.h
index e528ca954..f562775ee 100644
--- a/src/xbus/service.h
+++ b/src/xbus/service.h
@@ -225,7 +225,7 @@ namespace XBus
         double getSpeedBrakeRatio() const { return m_speedBrakeRatio.get(); }
 
     private:
-        CMessageBoxControl m_messages;
+        CMessageBoxControl m_messages { 128, 128, 16 };
         BlackMisc::Simulation::XPlane::CNavDataReferenceList m_airports;
         QTimer *m_airportUpdater = nullptr;
         void readAirportsDatabase();