diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Expression.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Expression.cs
index 9df0147..6f078c2 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Expression.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Expression.cs
@@ -97,7 +97,7 @@
 			}
 
 			// handle nulls
-			if (v == null)
+			if (v == null || v is String)
 			{
 				return 0;
 			}
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Save.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Save.cs
index b25dfb2..d4de99e 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Save.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Save.cs
@@ -841,7 +841,7 @@
                 var cellsWithoutFormulas = new HashSet<String>();
                 foreach (var c in worksheet.Internals.CellsCollection.GetCells())
                 {
-                    if (XLHelper.IsNullOrWhiteSpace(c.FormulaA1) || c.FormulaReference == null)
+                    if (XLHelper.IsNullOrWhiteSpace(c.FormulaA1) || (c.FormulaReference == null && c.FormulaA1.StartsWith("{")))
                         cellsWithoutFormulas.Add(c.Address.ToStringRelative());
                     else
                     {
@@ -4072,9 +4072,9 @@
                     }
 
                     cell.StyleIndex = styleId;
-                    if (opCell.HasFormula && opCell.FormulaReference != null)
+                    var formula = opCell.FormulaA1;
+                    if (opCell.HasFormula && !(formula.StartsWith("{") && opCell.FormulaReference == null))
                     {
-                        var formula = opCell.FormulaA1;
                         if (formula.StartsWith("{"))
                         {
                             formula = formula.Substring(1, formula.Length - 2);