diff --git a/src/generic/gridsel.cpp b/src/generic/gridsel.cpp
index fb478b339d..55de239323 100644
--- a/src/generic/gridsel.cpp
+++ b/src/generic/gridsel.cpp
@@ -749,7 +749,8 @@ wxArrayInt wxGridSelection::GetRowSelection() const
         {
             for ( int r = block.GetTopRow(); r <= block.GetBottomRow(); ++r )
             {
-                uniqueRows.Add(r);
+                if ( uniqueRows.Index(r) == wxNOT_FOUND )
+                    uniqueRows.Add(r);
             }
         }
     }
@@ -779,7 +780,8 @@ wxArrayInt wxGridSelection::GetColSelection() const
         {
             for ( int c = block.GetLeftCol(); c <= block.GetRightCol(); ++c )
             {
-                uniqueCols.Add(c);
+                if ( uniqueCols.Index(c) == wxNOT_FOUND )
+                    uniqueCols.Add(c);
             }
         }
     }
diff --git a/tests/controls/gridtest.cpp b/tests/controls/gridtest.cpp
index 3649985b36..34d4a925c5 100644
--- a/tests/controls/gridtest.cpp
+++ b/tests/controls/gridtest.cpp
@@ -901,6 +901,12 @@ TEST_CASE_METHOD(GridTestCase, "Grid::SelectionMode", "[grid]")
     CHECK(selectedRows.Count() == 1);
     CHECK(selectedRows[0] == 3);
 
+    // Check that overlapping selection blocks are handled correctly.
+    m_grid->ClearSelection();
+    m_grid->SelectBlock(0, 0, 4, 1);
+    m_grid->SelectBlock(2, 0, 6, 1, true /* add to selection */);
+    CHECK( m_grid->GetSelectedRows().size() == 7 );
+
     CHECK(m_grid->GetSelectionMode() == wxGrid::wxGridSelectRows);