1 files changed, 5 insertions, 1 deletions
diff --git a/xmlWorkbook.go b/xmlWorkbook.go
index 7151c6f..0e8839b 100644
--- a/xmlWorkbook.go
+++ b/xmlWorkbook.go
@@ -11,10 +11,14 @@
 
 package excelize
 
-import "encoding/xml"
+import (
+	"encoding/xml"
+	"sync"
+)
 
 // xlsxRelationships describe references from parts to other internal resources in the package or to external resources.
 type xlsxRelationships struct {
+	sync.Mutex
 	XMLName       xml.Name           `xml:"http://schemas.openxmlformats.org/package/2006/relationships Relationships"`
 	Relationships []xlsxRelationship `xml:"Relationship"`
 }