diff --git a/include/wx/gtk/slider.h b/include/wx/gtk/slider.h
index 0a34fcf729..b59afd3c8b 100644
--- a/include/wx/gtk/slider.h
+++ b/include/wx/gtk/slider.h
@@ -74,6 +74,8 @@ public:
     GtkWidget *m_scale;
 
 protected:
+    virtual wxSize DoGetBestSize() const wxOVERRIDE;
+
     GtkWidget *m_minLabel,*m_maxLabel;
     bool m_blockScrollEvent;
 
diff --git a/interface/wx/slider.h b/interface/wx/slider.h
index 9a4aa3df58..04cdb9a9ce 100644
--- a/interface/wx/slider.h
+++ b/interface/wx/slider.h
@@ -175,7 +175,15 @@ public:
             If ::wxDefaultPosition is specified then a default position is chosen.
         @param size
             Window size.
-            If ::wxDefaultSize is specified then a default size is chosen.
+            If ::wxDefaultSize is specified then a default size is chosen,
+            which is typically appropriate in the transverse slider direction,
+            but is just fixed 100 (DPI-independent) pixels in the primary
+            direction (i.e. vertical for ::wxSL_VERTICAL sliders or horizontal
+            for ::wxSL_HORIZONTAL ones), so it may be preferable to specify it
+            explicitly. Conversely, when using non-default size, it's usually
+            best to use @c -1 for the transverse size component, meaning that
+            the default should be used, as the appropriate value depends on the
+            platform and theme.
         @param style
             Window style. See wxSlider.
         @param validator
diff --git a/src/gtk/slider.cpp b/src/gtk/slider.cpp
index 3b59de161c..9d63d7a0e4 100644
--- a/src/gtk/slider.cpp
+++ b/src/gtk/slider.cpp
@@ -571,6 +571,16 @@ int wxSlider::GetTickFreq() const
 #endif
 }
 
+wxSize wxSlider::DoGetBestSize() const
+{
+    // We need to get the size in the transverse direction from GTK, but we use
+    // hard-coded default in the other direction, as otherwise the slider would
+    // have the smallest possible size and not have any extent at all.
+    wxSize size = GTKGetPreferredSize(m_widget);
+    (HasFlag(wxSL_VERTICAL) ? size.y : size.x) = 100;
+    return size;
+}
+
 GdkWindow *wxSlider::GTKGetWindow(wxArrayGdkWindows& WXUNUSED(windows)) const
 {
 #ifdef __WXGTK3__