diff --git a/include/wx/osx/cocoa/dataview.h b/include/wx/osx/cocoa/dataview.h
index 41d16201d8..e45ed0f358 100644
--- a/include/wx/osx/cocoa/dataview.h
+++ b/include/wx/osx/cocoa/dataview.h
@@ -557,6 +557,9 @@ private:
     wxCocoaOutlineDataSource* m_DataSource;
 
     wxCocoaOutlineView* m_OutlineView;
+
+    // Width of expander in pixels, computed on demand.
+    int m_expanderWidth;
 };
 
 #endif // _WX_DATAVIEWCTRL_COCOOA_H_
diff --git a/include/wx/osx/dataview.h b/include/wx/osx/dataview.h
index a7a58d6f54..80e6aa0e99 100644
--- a/include/wx/osx/dataview.h
+++ b/include/wx/osx/dataview.h
@@ -306,7 +306,7 @@ private:
 
   wxDataViewColumnPtrArrayType m_ColumnPtrs; // all column pointers are stored in an array
 
-  wxDataViewModelNotifier* m_ModelNotifier; // stores the model notifier for the control (does not own the notifier)
+  class wxOSXDataViewModelNotifier* m_ModelNotifier; // stores the model notifier for the control (does not own the notifier)
 
  // wxWidget internal stuff:
   wxDECLARE_DYNAMIC_CLASS(wxDataViewCtrl);
diff --git a/src/osx/cocoa/dataview.mm b/src/osx/cocoa/dataview.mm
index 770719e4a9..9f927f6abf 100644
--- a/src/osx/cocoa/dataview.mm
+++ b/src/osx/cocoa/dataview.mm
@@ -2045,7 +2045,8 @@ wxCocoaDataViewControl::wxCocoaDataViewControl(wxWindow* peer,
         [[NSScrollView alloc] initWithFrame:wxOSXGetFrameForControl(peer,pos,size)]
       ),
       m_DataSource(NULL),
-      m_OutlineView([[wxCocoaOutlineView alloc] init])
+      m_OutlineView([[wxCocoaOutlineView alloc] init]),
+      m_expanderWidth(0)
 {
     // initialize scrollview (the outline view is part of a scrollview):
     NSScrollView* scrollview = (NSScrollView*) GetWXWidget();
@@ -2175,7 +2176,9 @@ void wxCocoaDataViewControl::FitColumnWidthToContent(unsigned int pos)
             : m_width(0),
               m_view(view),
               m_column(columnIndex),
-              m_indent(0)
+              m_indent(0),
+              m_expander(0),
+              m_tableColumn(column)
         {
             // account for indentation in the column with expander
             if ( column == [m_view outlineTableColumn] )
@@ -2193,18 +2196,27 @@ void wxCocoaDataViewControl::FitColumnWidthToContent(unsigned int pos)
             unsigned cellWidth = [cell cellSize].width + 1/*round the float up*/;
 
             if ( m_indent )
-                cellWidth += m_indent * ([m_view levelForRow:row] + 1);
+                cellWidth += m_indent * [m_view levelForRow:row];
+
+            if ( m_expander == 0 && m_tableColumn == [m_view outlineTableColumn] )
+            {
+                NSRect rc = [m_view frameOfOutlineCellAtRow:row];
+                m_expander = ceil(rc.origin.x + rc.size.width);
+            }
 
             m_width = wxMax(m_width, cellWidth);
         }
 
         int GetMaxWidth() const { return m_width; }
+        int GetExpanderWidth() const { return m_expander; }
 
     private:
         int m_width;
         wxCocoaOutlineView *m_view;
         unsigned m_column;
         int m_indent;
+        int m_expander;
+        NSTableColumn *m_tableColumn;
     };
 
     MaxWidthCalculator calculator(m_OutlineView, column, pos);
@@ -2275,7 +2287,12 @@ void wxCocoaDataViewControl::FitColumnWidthToContent(unsigned int pos)
                    count);
     }
 
-    [column setWidth:calculator.GetMaxWidth()];
+    // there might not necessarily be an expander in the rows we've examined above so let's
+    // globally store the expander width for re-use because it should always be the same
+    if ( m_expanderWidth == 0 )
+        m_expanderWidth = calculator.GetExpanderWidth();
+
+    [column setWidth:calculator.GetMaxWidth() + m_expanderWidth];
 }
 
 //
diff --git a/src/osx/dataview_osx.cpp b/src/osx/dataview_osx.cpp
index ad197cc85c..7fc3dec650 100644
--- a/src/osx/dataview_osx.cpp
+++ b/src/osx/dataview_osx.cpp
@@ -73,14 +73,15 @@ public:
   virtual bool Cleared() wxOVERRIDE;
   virtual void Resort() wxOVERRIDE;
 
+ // adjust wxCOL_WIDTH_AUTOSIZE columns to fit the data
+  void AdjustAutosizedColumns();
+
 protected:
  // if the dataview control can have a variable row height this method sets the dataview's control row height of
  // the passed item to the maximum value occupied by the item in all columns
   void AdjustRowHeight(wxDataViewItem const& item);
  // ... and the same method for a couple of items:
   void AdjustRowHeights(wxDataViewItemArray const& items);
- // adjust wxCOL_WIDTH_AUTOSIZE columns to fit the data
-  void AdjustAutosizedColumns();
 
 private:
   wxDataViewCtrl* m_DataViewCtrlPtr;
@@ -505,6 +506,9 @@ int wxDataViewCtrl::GetColumnPosition(wxDataViewColumn const* columnPtr) const
 void wxDataViewCtrl::Collapse(wxDataViewItem const& item)
 {
   GetDataViewPeer()->Collapse(item);
+
+  if ( m_ModelNotifier )
+    m_ModelNotifier->AdjustAutosizedColumns();
 }
 
 void wxDataViewCtrl::EnsureVisible(wxDataViewItem const& item, wxDataViewColumn const* columnPtr)
@@ -518,7 +522,10 @@ void wxDataViewCtrl::EnsureVisible(wxDataViewItem const& item, wxDataViewColumn
 
 void wxDataViewCtrl::DoExpand(wxDataViewItem const& item)
 {
-  return GetDataViewPeer()->DoExpand(item);
+  GetDataViewPeer()->DoExpand(item);
+
+  if ( m_ModelNotifier )
+    m_ModelNotifier->AdjustAutosizedColumns();
 }
 
 bool wxDataViewCtrl::IsExpanded( const wxDataViewItem & item ) const