diff --git a/src/Gui/Quarter/InputDevice.cpp b/src/Gui/Quarter/InputDevice.cpp
index 69a6e74e43..a29d74d7fa 100644
--- a/src/Gui/Quarter/InputDevice.cpp
+++ b/src/Gui/Quarter/InputDevice.cpp
@@ -48,7 +48,7 @@ using namespace SIM::Coin3D::Quarter;
   devices.
 */
 
-InputDevice::InputDevice(void)
+InputDevice::InputDevice(void) : quarter(nullptr)
 {
   this->mousepos = SbVec2s(0, 0);
 }
diff --git a/src/Gui/Quarter/Mouse.cpp b/src/Gui/Quarter/Mouse.cpp
index 41cc5b5c46..f64b0a530d 100644
--- a/src/Gui/Quarter/Mouse.cpp
+++ b/src/Gui/Quarter/Mouse.cpp
@@ -55,6 +55,9 @@
 #include <Inventor/SbVec2s.h>
 #include <Inventor/events/SoEvents.h>
 #include <Inventor/errors/SoDebugError.h>
+#if QT_VERSION >= 0x050000
+#include <Quarter/QuarterWidget.h>
+#endif
 
 namespace SIM { namespace Coin3D { namespace Quarter {
 
diff --git a/src/Gui/Quarter/QuarterWidget.cpp b/src/Gui/Quarter/QuarterWidget.cpp
index c2e1f805ae..529be0b874 100644
--- a/src/Gui/Quarter/QuarterWidget.cpp
+++ b/src/Gui/Quarter/QuarterWidget.cpp
@@ -835,7 +835,7 @@ void QuarterWidget::resizeEvent(QResizeEvent* event)
 */
 void QuarterWidget::paintEvent(QPaintEvent* event)
 {
-    if(updateDevicePixelRatio()) {
+    if (updateDevicePixelRatio()) {
         qreal dev_pix_ratio = devicePixelRatio();
         int width = static_cast<int>(dev_pix_ratio * this->width());
         int height = static_cast<int>(dev_pix_ratio * this->height());
diff --git a/src/Gui/Quarter/devices/InputDevice.h b/src/Gui/Quarter/devices/InputDevice.h
index e09105e6f7..bf2785d1eb 100644
--- a/src/Gui/Quarter/devices/InputDevice.h
+++ b/src/Gui/Quarter/devices/InputDevice.h
@@ -35,7 +35,6 @@
 
 #include <Quarter/Basic.h>
 #include <Inventor/SbVec2s.h>
-#include <Quarter/QuarterWidget.h>
 
 class QEvent;
 class SoEvent;
@@ -43,6 +42,8 @@ class QInputEvent;
 
 namespace SIM { namespace Coin3D { namespace Quarter {
 
+class QuarterWidget;
+
 class QUARTER_DLL_API InputDevice {
 public:
   InputDevice(QuarterWidget * quarter);