diff --git a/src/gtk/toplevel.cpp b/src/gtk/toplevel.cpp
index 8a294525a4..3f8b6b74ed 100644
--- a/src/gtk/toplevel.cpp
+++ b/src/gtk/toplevel.cpp
@@ -919,7 +919,7 @@ void wxTopLevelWindowGTK::DoGetClientSize( int *width, int *height ) const
 
     if (height)
     {
-        *height = m_height - 2 * m_miniEdge + m_miniTitle;
+        *height = m_height - 2 * m_miniEdge - m_miniTitle;
         if (*height < 0)
             *height = 0;
     }