diff --git a/include/wx/generic/grid.h b/include/wx/generic/grid.h
index d4e403e8eb..d753161100 100644
--- a/include/wx/generic/grid.h
+++ b/include/wx/generic/grid.h
@@ -2325,13 +2325,13 @@ protected:
 
     // this function is called to extend the block being currently selected
     // from mouse and keyboard event handlers
-    void UpdateBlockBeingSelected(int topRow, int leftCol,
-                                  int bottomRow, int rightCol);
+    void UpdateBlockBeingSelected(int blockStartRow, int blockStartCol,
+                                  int blockEndRow, int blockEndCol);
 
-    void UpdateBlockBeingSelected(const wxGridCellCoords& topLeft,
-                        const wxGridCellCoords& bottomRight)
-        { UpdateBlockBeingSelected(topLeft.GetRow(), topLeft.GetCol(),
-                         bottomRight.GetRow(), bottomRight.GetCol()); }
+    void UpdateBlockBeingSelected(const wxGridCellCoords& blockStart,
+                                  const wxGridCellCoords& blockEnd)
+        { UpdateBlockBeingSelected(blockStart.GetRow(), blockStart.GetCol(),
+                                   blockEnd.GetRow(), blockEnd.GetCol()); }
 
     virtual bool ShouldScrollToChildOnFocus(wxWindow* WXUNUSED(win)) wxOVERRIDE
         { return false; }
diff --git a/src/generic/grid.cpp b/src/generic/grid.cpp
index c1dbb96548..97a493056e 100644
--- a/src/generic/grid.cpp
+++ b/src/generic/grid.cpp
@@ -5822,11 +5822,16 @@ bool wxGrid::SetCurrentCell( const wxGridCellCoords& coords )
 }
 
 void
-wxGrid::UpdateBlockBeingSelected(int topRow, int leftCol,
-                                 int bottomRow, int rightCol)
+wxGrid::UpdateBlockBeingSelected(int blockStartRow, int blockStartCol,
+                                 int blockEndRow, int blockEndCol)
 {
+    m_selectedBlockCorner = wxGridCellCoords(blockEndRow, blockEndCol);
     MakeCellVisible(m_selectedBlockCorner);
-    m_selectedBlockCorner = wxGridCellCoords(bottomRow, rightCol);
+
+    int topRow = wxMin(blockStartRow, blockEndRow);
+    int leftCol = wxMin(blockStartCol, blockEndCol);
+    int bottomRow = wxMax(blockStartRow, blockEndRow);
+    int rightCol = wxMax(blockStartCol, blockEndCol);
 
     if ( m_selection )
     {
@@ -5864,9 +5869,6 @@ wxGrid::UpdateBlockBeingSelected(int topRow, int leftCol,
         }
     }
 
-    EnsureFirstLessThanSecond(topRow, bottomRow);
-    EnsureFirstLessThanSecond(leftCol, rightCol);
-
     wxGridCellCoords updateTopLeft = wxGridCellCoords(topRow, leftCol),
                      updateBottomRight = wxGridCellCoords(bottomRow, rightCol);