diff --git a/gui/CMakeLists.txt b/gui/CMakeLists.txt
index 4fce71d..c36b10a 100644
--- a/gui/CMakeLists.txt
+++ b/gui/CMakeLists.txt
@@ -10,17 +10,20 @@ include_directories (
 # Run Qt's moc automatically.
 set (CMAKE_AUTOMOC ON)
 
-find_package (Qt5Widgets)
+find_package(Qt6 COMPONENTS Core Widgets)
+if (NOT Qt6_FOUND)
+    find_package(Qt5 5.15 REQUIRED COMPONENTS Core Widgets)
+endif()
 
 configure_file (gui_info.rc.in gui_info.rc)
 
 if (POLOLU_BUILD)
   if (APPLE)
     # Embed app.icns in the executable.
-    qt5_add_resources(ICON_QRC qt/app_icns.qrc)
+    qt_add_resources(ICON_QRC qt/app_icns.qrc)
   else ()
     # Embed app.ico in the executable.
-    qt5_add_resources(ICON_QRC qt/app_ico.qrc)
+    qt_add_resources(ICON_QRC qt/app_ico.qrc)
   endif ()
 endif ()
 
@@ -50,6 +53,6 @@ if (WIN32)
   )
 endif ()
 
-target_link_libraries (gui Qt5::Widgets lib bootloader)
+target_link_libraries (gui Qt::Widgets lib bootloader)
 
 install(TARGETS gui DESTINATION bin)
diff --git a/gui/qt/main_window.cpp b/gui/qt/main_window.cpp
index 86f1188..5c76abc 100644
--- a/gui/qt/main_window.cpp
+++ b/gui/qt/main_window.cpp
@@ -13,7 +13,6 @@
 #include <QCloseEvent>
 #include <QComboBox>
 #include <QDesktopServices>
-#include <QDesktopWidget>
 #include <QDoubleSpinBox>
 #include <QFileDialog>
 #include <QGridLayout>
@@ -1365,7 +1364,7 @@ void main_window::center_at_startup_if_needed()
         Qt::LeftToRight,
         Qt::AlignCenter,
         size(),
-        qApp->desktop()->availableGeometry()
+        qApp->primaryScreen()->availableGeometry()
         )
       );
   }