diff --git a/src/gui/C4StartupOptionsDlg.cpp b/src/gui/C4StartupOptionsDlg.cpp
index bcbbbd885..6e7e39695 100644
--- a/src/gui/C4StartupOptionsDlg.cpp
+++ b/src/gui/C4StartupOptionsDlg.cpp
@@ -23,6 +23,7 @@
 #include "graphics/C4Draw.h"
 #include "graphics/C4GraphicsResource.h"
 #include "gui/C4MouseControl.h"
+#include "gui/C4KeyboardInput.h"
 #include "gui/C4StartupMainDlg.h"
 #include "network/C4Network2.h"
 #include "platform/C4GamePadCon.h"
@@ -147,7 +148,17 @@ C4StartupOptionsDlg::KeySelDialog::KeySelDialog(const C4PlayerControlAssignment
 	: C4GUI::MessageDialog(GetDlgMessage(assignment, assignment_set).getData(), LoadResStr("IDS_MSG_DEFINEKEY"), C4GUI::MessageDialog::btnAbort | C4GUI::MessageDialog::btnReset, GetDlgIcon(assignment_set), C4GUI::MessageDialog::dsRegular),
 		key(KEY_Undefined), assignment(assignment), assignment_set(assignment_set)
 {
-	pKeyListener = new C4KeyBinding(C4KeyCodeEx(KEY_Any, KEYS_None), "DefineKey", KEYSCOPE_Gui, new C4GUI::DlgKeyCBPassKey<C4StartupOptionsDlg::KeySelDialog>(*this, &C4StartupOptionsDlg::KeySelDialog::KeyDown), C4CustomKey::PRIO_PlrControl);
+	pKeyListener = new C4KeyBinding(
+		C4KeyCodeEx(KEY_Any, KEYS_None),
+		"DefineKey",
+		KEYSCOPE_Gui,
+		new C4GUI::DlgKeyCBPassKey<C4StartupOptionsDlg::KeySelDialog>(
+			*this,
+			&C4StartupOptionsDlg::KeySelDialog::KeyDown,
+			&C4StartupOptionsDlg::KeySelDialog::KeyUp
+		),
+		C4CustomKey::PRIO_PlrControl
+	);
 }
 
 StdStrBuf C4StartupOptionsDlg::KeySelDialog::GetDlgMessage(const C4PlayerControlAssignment *assignment, const C4PlayerControlAssignmentSet *assignment_set)
@@ -183,7 +194,61 @@ C4StartupOptionsDlg::KeySelDialog::~KeySelDialog()
 	delete pKeyListener;
 }
 
-bool C4StartupOptionsDlg::KeySelDialog::KeyDown(const C4KeyCodeEx &key)
+void C4StartupOptionsDlg::KeySelDialog::MouseInput(C4GUI::CMouse& rMouse, int32_t iButton, int32_t iX, int32_t iY, DWORD dwKeyParam)
+{
+	// Original action
+	C4GUI::MessageDialog::MouseInput(rMouse, iButton, iX, iY, dwKeyParam);
+
+	// Find out to where the input was made (code duplication with C4GUI::Window::MouseInput)
+	// get client pos
+	C4Rect &rcClientRect = GetClientRect(), &rcBounds = GetBounds();
+	iX -= rcClientRect.x - rcBounds.x; iY -= rcClientRect.y - rcBounds.y;
+	// forward to topmost child element
+	for (Element *pChild = pLast; pChild; pChild = pChild->GetPrev())
+		if (pChild->fVisible && pChild->GetBounds().Contains(iX, iY))
+		{
+			if (dynamic_cast<C4GUI::Label*>(pChild))
+				break;
+			else
+				return;
+		}
+	// Only process the input event if the user certainly didn't click a button or anything…
+
+	// Logic duplication of C4PlayerControl::DoMouseInput (and C4MouseControl::Move for the wheel_dir.) There has to be a better way. :(
+	uint8_t mouseevent_code;
+	int wheel_dir = 0;
+	if (iButton == C4MC_Button_Wheel) wheel_dir = (short)(dwKeyParam >> 16);
+	switch (iButton)
+	{
+	case C4MC_Button_LeftUp:
+	case C4MC_Button_RightUp:
+	case C4MC_Button_MiddleUp:
+	case C4MC_Button_X1Up:
+	case C4MC_Button_X2Up:
+	case C4MC_Button_None:
+		return;
+	case C4MC_Button_LeftDown: mouseevent_code = KEY_MOUSE_ButtonLeft; break;
+	case C4MC_Button_LeftDouble: mouseevent_code = KEY_MOUSE_ButtonLeftDouble; break;
+	case C4MC_Button_RightDown: mouseevent_code = KEY_MOUSE_ButtonRight; break;
+	case C4MC_Button_RightDouble: mouseevent_code = KEY_MOUSE_ButtonRightDouble; break;
+	case C4MC_Button_MiddleDown: mouseevent_code = KEY_MOUSE_ButtonMiddle; break;
+	case C4MC_Button_MiddleDouble: mouseevent_code = KEY_MOUSE_ButtonMiddleDouble; break;
+	case C4MC_Button_X1Down: mouseevent_code = KEY_MOUSE_ButtonX1; break;
+	case C4MC_Button_X1Double: mouseevent_code = KEY_MOUSE_ButtonX1Double; break;
+	case C4MC_Button_X2Down: mouseevent_code = KEY_MOUSE_ButtonX2; break;
+	case C4MC_Button_X2Double: mouseevent_code = KEY_MOUSE_ButtonX2Double; break;
+	case C4MC_Button_Wheel:
+		if (!wheel_dir) return;
+		mouseevent_code = (wheel_dir > 0) ? KEY_MOUSE_Wheel1Up : KEY_MOUSE_Wheel1Down; break;
+	}
+	C4KeyCodeEx key{KEY_Mouse(0, mouseevent_code), KEYS_None};
+	if (dwKeyParam & MK_CONTROL) key.dwShift |= KEYS_Control;
+	if (dwKeyParam & MK_SHIFT) key.dwShift |= KEYS_Shift;
+	if (dwKeyParam & MK_ALT) key.dwShift |= KEYS_Alt;
+	KeyDown(key);
+}
+
+bool C4StartupOptionsDlg::KeySelDialog::KeyPress(const C4KeyCodeEx &key, bool fDown)
 {
 	// safety
 	if (!assignment || !assignment_set) return false;
@@ -200,6 +265,13 @@ bool C4StartupOptionsDlg::KeySelDialog::KeyDown(const C4KeyCodeEx &key)
 	{
 		if (!assignment_set->HasKeyboard()) return false;
 	}
+	// FIXME: There doesn't seem to be any kind of KEY_IsModifier function…
+	switch (key.Key) {
+		case K_CONTROL_L: case K_SHIFT_L: case K_ALT_L:
+		case K_CONTROL_R: case K_SHIFT_R: case K_ALT_R:
+			if (fDown)
+				return false;
+	}
 	// okay, use it
 	this->key=key;
 	Close(true);
diff --git a/src/gui/C4StartupOptionsDlg.h b/src/gui/C4StartupOptionsDlg.h
index 689be61db..740adf86a 100644
--- a/src/gui/C4StartupOptionsDlg.h
+++ b/src/gui/C4StartupOptionsDlg.h
@@ -165,7 +165,10 @@ private:
 		static C4GUI::Icons GetDlgIcon(const class C4PlayerControlAssignmentSet *assignment_set);
 
 	protected:
-		bool KeyDown(const C4KeyCodeEx &key);
+		bool KeyDown(const C4KeyCodeEx &key) { return KeyPress(key, true); };
+		bool KeyUp(const C4KeyCodeEx &key) { return KeyPress(key, false); };
+		bool KeyPress(const C4KeyCodeEx &key, bool fDown);
+		void MouseInput(C4GUI::CMouse &rMouse, int32_t iButton, int32_t iX, int32_t iY, DWORD dwKeyParam) override;
 	public:
 		KeySelDialog(const class C4PlayerControlAssignment *assignment, const class C4PlayerControlAssignmentSet *assignment_set);
 		~KeySelDialog() override;