diff --git a/CMakeLists.txt b/CMakeLists.txt
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -4,7 +4,7 @@
 set(PROJECT_VERSION "5.11.90")
 set(PROJECT_VERSION_MAJOR 5)
 
-set(QT_MIN_VERSION "5.7.0")
+set(QT_MIN_VERSION "5.9.0")
 set(KF5_MIN_VERSION "5.34.0")
 
 set(CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules ${CMAKE_MODULE_PATH} )
@@ -250,13 +250,9 @@
                        TYPE OPTIONAL)
 
 # dependencies for QPA plugin
-if(Qt5Core_VERSION VERSION_LESS "5.8.0")
-    find_package(Qt5PlatformSupport REQUIRED)
-else()
-    find_package(Qt5FontDatabaseSupport REQUIRED)
-    find_package(Qt5ThemeSupport REQUIRED)
-    find_package(Qt5EventDispatcherSupport REQUIRED)
-endif()
+find_package(Qt5FontDatabaseSupport REQUIRED)
+find_package(Qt5ThemeSupport REQUIRED)
+find_package(Qt5EventDispatcherSupport REQUIRED)
 
 find_package(Freetype REQUIRED)
 set_package_properties(Freetype PROPERTIES DESCRIPTION "A font rendering engine"
diff --git a/plugins/kdecorations/aurorae/themes/plastik/code/plastikbutton.cpp b/plugins/kdecorations/aurorae/themes/plastik/code/plastikbutton.cpp
--- a/plugins/kdecorations/aurorae/themes/plastik/code/plastikbutton.cpp
+++ b/plugins/kdecorations/aurorae/themes/plastik/code/plastikbutton.cpp
@@ -281,9 +281,7 @@
             drawObject(p, HorizontalLine, r.x()+(r.width()-lwMark)/2, r.y()+(r.height()-lwMark)/2, lwMark, lwMark);
 
             // Fall through to OnAllDesktopsIcon intended!
-#if (QT_VERSION >= QT_VERSION_CHECK(5, 8, 0))
             Q_FALLTHROUGH();
-#endif
         }
         case OnAllDesktopsIcon:
         {
@@ -309,9 +307,7 @@
                 drawObject(p, HorizontalLine, center-(lwArrow-2), r.y()+2*lwArrow, (lwArrow-2)*2, lwArrow);
 
             // Fall through to KeepAboveIcon intended!
-#if (QT_VERSION >= QT_VERSION_CHECK(5, 8, 0))
             Q_FALLTHROUGH();
-#endif
         }
         case KeepAboveIcon:
         {
@@ -337,9 +333,7 @@
                 drawObject(p, HorizontalLine, center-(lwArrow-2), r.bottom()-(lwArrow-1)-2*lwArrow, (lwArrow-2)*2, lwArrow);
 
             // Fall through to KeepBelowIcon intended!
-#if (QT_VERSION >= QT_VERSION_CHECK(5, 8, 0))
             Q_FALLTHROUGH();
-#endif
         }
         case KeepBelowIcon:
         {
diff --git a/plugins/platforms/x11/standalone/x11_platform.cpp b/plugins/platforms/x11/standalone/x11_platform.cpp
--- a/plugins/platforms/x11/standalone/x11_platform.cpp
+++ b/plugins/platforms/x11/standalone/x11_platform.cpp
@@ -116,9 +116,7 @@
         } else {
             qCWarning(KWIN_X11STANDALONE) << "Glx not available, trying EGL instead.";
             // no break, needs fall-through
-#if (QT_VERSION >= QT_VERSION_CHECK(5, 8, 0))
             Q_FALLTHROUGH();
-#endif
         }
 #endif
     case EglPlatformInterface:
@@ -236,9 +234,7 @@
         group.writeEntry(unsafeKey, true);
         group.sync();
         // Deliberately continue with PreFrame
-#if (QT_VERSION >= QT_VERSION_CHECK(5, 8, 0))
         Q_FALLTHROUGH();
-#endif
     case OpenGLSafePoint::PreFrame:
         if (m_openGLFreezeProtectionThread == nullptr) {
             Q_ASSERT(m_openGLFreezeProtection == nullptr);
@@ -267,9 +263,7 @@
         group.writeEntry(unsafeKey, false);
         group.sync();
         // Deliberately continue with PostFrame
-#if (QT_VERSION >= QT_VERSION_CHECK(5, 8, 0))
         Q_FALLTHROUGH();
-#endif
     case OpenGLSafePoint::PostFrame:
         QMetaObject::invokeMethod(m_openGLFreezeProtection, "stop", Qt::QueuedConnection);
         break;
diff --git a/plugins/qpa/integration.cpp b/plugins/qpa/integration.cpp
--- a/plugins/qpa/integration.cpp
+++ b/plugins/qpa/integration.cpp
@@ -47,15 +47,9 @@
 #include <qpa/qwindowsysteminterface.h>
 #include <QtCore/private/qeventdispatcher_unix_p.h>
 
-#if QT_VERSION >= 0x050800
 #include <QtFontDatabaseSupport/private/qgenericunixfontdatabase_p.h>
 #include <QtThemeSupport/private/qgenericunixthemes_p.h>
 #include <QtEventDispatcherSupport/private/qunixeventdispatcher_qpa_p.h>
-#else
-#include <QtPlatformSupport/private/qgenericunixfontdatabase_p.h>
-#include <QtPlatformSupport/private/qgenericunixthemes_p.h>
-#include <QtPlatformSupport/private/qunixeventdispatcher_qpa_p.h>
-#endif
 
 namespace KWin
 {
diff --git a/plugins/scenes/opengl/scene_opengl.cpp b/plugins/scenes/opengl/scene_opengl.cpp
--- a/plugins/scenes/opengl/scene_opengl.cpp
+++ b/plugins/scenes/opengl/scene_opengl.cpp
@@ -448,9 +448,7 @@
             if (strstr(message, "Buffer detailed info:") && strstr(message, "has been updated"))
                 scheduleVboReInit();
             // fall through! for general message printing
-#if (QT_VERSION >= QT_VERSION_CHECK(5, 8, 0))
             Q_FALLTHROUGH();
-#endif
         case GL_DEBUG_TYPE_DEPRECATED_BEHAVIOR:
         case GL_DEBUG_TYPE_PORTABILITY:
         case GL_DEBUG_TYPE_PERFORMANCE: