diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Save.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Save.cs
index 40cf60a..914086e 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Save.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/XLWorkbook_Save.cs
@@ -197,11 +197,16 @@
             
 
             var partsToRemove = workbookPart.Parts.Where(s => worksheets.Deleted.Contains(s.RelationshipId)).ToList();
-            var pivotCacheDefinitionsToRemove = partsToRemove.SelectMany(s => ((WorksheetPart)s.OpenXmlPart).PivotTableParts.Select(pt => pt.PivotTableCacheDefinitionPart)).Distinct().ToList();
-            var pivotCachesToRemove = workbookPart.Workbook.PivotCaches.Where(pc => pivotCacheDefinitionsToRemove.Select(pcd => workbookPart.GetIdOfPart(pcd)).ToList().Contains(((PivotCache)pc).Id)).Distinct().ToList();
 
+            var pivotCacheDefinitionsToRemove = partsToRemove.SelectMany(s => ((WorksheetPart)s.OpenXmlPart).PivotTableParts.Select(pt => pt.PivotTableCacheDefinitionPart)).Distinct().ToList();
             pivotCacheDefinitionsToRemove.ForEach(c => workbookPart.DeletePart(c));
-            pivotCachesToRemove.ForEach(c => workbookPart.Workbook.PivotCaches.RemoveChild(c));
+
+            if (workbookPart.Workbook != null && workbookPart.Workbook.PivotCaches != null)
+            {
+                var pivotCachesToRemove = workbookPart.Workbook.PivotCaches.Where(pc => pivotCacheDefinitionsToRemove.Select(pcd => workbookPart.GetIdOfPart(pcd)).ToList().Contains(((PivotCache)pc).Id)).Distinct().ToList();
+                pivotCachesToRemove.ForEach(c => workbookPart.Workbook.PivotCaches.RemoveChild(c));
+            }
+
             worksheets.Deleted.ToList().ForEach(ws => DeleteSheetAndDependencies(workbookPart, ws));
 
             context.RelIdGenerator.AddValues(workbookPart.Parts.Select(p => p.RelationshipId).ToList(), RelType.Workbook);