diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Load.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Load.cs
index 9ec97e6..1a3babf 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Load.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Load.cs
@@ -188,6 +188,7 @@
                                         (Columns)reader.LoadCurrentElement());
                         else if (reader.ElementType == typeof(Row))
                         {
+                            lastRow = 0;
                             LoadRows(s, numberingFormats, fills, borders, fonts, ws, sharedStrings, sharedFormulasR1C1,
                                      styleList, (Row)reader.LoadCurrentElement());
                         }
@@ -716,12 +717,17 @@
             sheetArea = sections[1];
         }
 
+        private Int32 lastCell;
         private void LoadCells(SharedStringItem[] sharedStrings, Stylesheet s, NumberingFormats numberingFormats,
                                Fills fills, Borders borders, Fonts fonts, Dictionary<uint, string> sharedFormulasR1C1,
-                               XLWorksheet ws, Dictionary<Int32, IXLStyle> styleList, Cell cell)
+                               XLWorksheet ws, Dictionary<Int32, IXLStyle> styleList, Cell cell, Int32 rowIndex)
         {
             Int32 styleIndex = cell.StyleIndex != null ? Int32.Parse(cell.StyleIndex.InnerText) : 0;
-            var xlCell = ws.CellFast(cell.CellReference);
+
+            String cellReference = cell.CellReference == null
+                                       ? XLHelper.GetColumnLetterFromNumber(++lastCell) + rowIndex
+                                       : cell.CellReference.Value;
+            var xlCell = ws.CellFast(cellReference);
 
             if (styleList.ContainsKey(styleIndex))
                 xlCell.Style = styleList[styleIndex];
@@ -985,12 +991,14 @@
             fontBase.VerticalAlignment = verticalTextAlignment.Val != null ? verticalTextAlignment.Val.Value.ToClosedXml() : XLFontVerticalTextAlignmentValues.Baseline;
         }
 
+        private Int32 lastRow;
         private void LoadRows(Stylesheet s, NumberingFormats numberingFormats, Fills fills, Borders borders, Fonts fonts,
                               XLWorksheet ws, SharedStringItem[] sharedStrings,
                               Dictionary<uint, string> sharedFormulasR1C1, Dictionary<Int32, IXLStyle> styleList,
                               Row row)
         {
-            var xlRow = ws.Row((Int32) row.RowIndex.Value, false);
+            Int32 rowIndex = row.RowIndex == null ? ++lastRow : (Int32) row.RowIndex.Value;
+            var xlRow = ws.Row(rowIndex, false);
             
             if (row.Height != null)
                 xlRow.Height = row.Height;
@@ -1021,9 +1029,10 @@
                 }
             }
 
+            lastCell = 0;
             foreach (Cell cell in row.Elements<Cell>())
                 LoadCells(sharedStrings, s, numberingFormats, fills, borders, fonts, sharedFormulasR1C1, ws, styleList,
-                          cell);
+                          cell, rowIndex);
         }
 
         private void LoadColumns(Stylesheet s, NumberingFormats numberingFormats, Fills fills, Borders borders,
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Save.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Save.cs
index 8cfe1f4..b6ec68e 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Save.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Save.cs
@@ -3934,7 +3934,8 @@
                 cellsByRow[rowNum].Add(c);
             }
 
-            var sheetDataRows = sheetData.Elements<Row>().ToDictionary(r => (Int32) r.RowIndex.Value, r => r);
+            Int32 lastRow = 0;
+            var sheetDataRows = sheetData.Elements<Row>().ToDictionary(r => r.RowIndex == null ? ++lastRow : (Int32) r.RowIndex.Value, r => r);
             foreach (
                 var r in
                     xlWorksheet.Internals.RowsCollection.Deleted.Where(r => sheetDataRows.ContainsKey(r.Key)))
@@ -4005,8 +4006,10 @@
                         row.OutlineLevel = (byte) thisRow.OutlineLevel;
                 }
 
-
-                var cellsByReference = row.Elements<Cell>().ToDictionary(c => c.CellReference.Value, c => c);
+                Int32 lastCell = 0;
+                var cellsByReference = row.Elements<Cell>().ToDictionary(c => c.CellReference == null
+                                       ? XLHelper.GetColumnLetterFromNumber(++lastCell) + distinctRow
+                                       : c.CellReference.Value, c => c);
 
                 foreach (var c in xlWorksheet.Internals.CellsCollection.Deleted.ToList())
                 {