diff --git a/src/gtk/window.cpp b/src/gtk/window.cpp
index 8947ad7008..b9f735e9aa 100644
--- a/src/gtk/window.cpp
+++ b/src/gtk/window.cpp
@@ -1434,6 +1434,7 @@ template<typename T> void InitMouseEvent(wxWindowGTK *win,
     if (event.GetEventType() == wxEVT_MOUSEWHEEL)
     {
        event.m_linesPerAction = 3;
+       event.m_wheelDelta = 120;
        if (((GdkEventButton*)gdk_event)->button == 4)
            event.m_wheelRotation = 120;
        else if (((GdkEventButton*)gdk_event)->button == 5)
@@ -1921,6 +1922,7 @@ static gint gtk_window_wheel_callback (GtkWidget * widget,
     event.m_middleDown = (gdk_event->state & GDK_BUTTON2_MASK);
     event.m_rightDown = (gdk_event->state & GDK_BUTTON3_MASK);
     event.m_linesPerAction = 3;
+    event.m_wheelDelta = 120;
     if (gdk_event->direction == GDK_SCROLL_UP)
         event.m_wheelRotation = 120;
     else
diff --git a/src/gtk1/window.cpp b/src/gtk1/window.cpp
index 8947ad7008..b9f735e9aa 100644
--- a/src/gtk1/window.cpp
+++ b/src/gtk1/window.cpp
@@ -1434,6 +1434,7 @@ template<typename T> void InitMouseEvent(wxWindowGTK *win,
     if (event.GetEventType() == wxEVT_MOUSEWHEEL)
     {
        event.m_linesPerAction = 3;
+       event.m_wheelDelta = 120;
        if (((GdkEventButton*)gdk_event)->button == 4)
            event.m_wheelRotation = 120;
        else if (((GdkEventButton*)gdk_event)->button == 5)
@@ -1921,6 +1922,7 @@ static gint gtk_window_wheel_callback (GtkWidget * widget,
     event.m_middleDown = (gdk_event->state & GDK_BUTTON2_MASK);
     event.m_rightDown = (gdk_event->state & GDK_BUTTON3_MASK);
     event.m_linesPerAction = 3;
+    event.m_wheelDelta = 120;
     if (gdk_event->direction == GDK_SCROLL_UP)
         event.m_wheelRotation = 120;
     else