diff --git a/sort.go b/sort.go
index b9f1f49..1d34b4c 100644
--- a/sort.go
+++ b/sort.go
@@ -4,7 +4,11 @@
 package multierror
 
 // Len implements sort.Interface function for length
-func (err Error) Len() int {
+func (err *Error) Len() int {
+	if err == nil {
+		return 0
+	}
+
 	return len(err.Errors)
 }