diff --git a/builder/xenserver/iso/builder.go b/builder/xenserver/iso/builder.go
index a9e37f1..d39a2bf 100644
--- a/builder/xenserver/iso/builder.go
+++ b/builder/xenserver/iso/builder.go
@@ -40,7 +40,7 @@ func (self *Builder) Prepare(raws ...interface{}) (params []string, warns []stri
 	}, raws...)
 
 	if err != nil {
-		packer.MultiErrorAppend(errs, err)
+		errs = packer.MultiErrorAppend(errs, err)
 	}
 
 	errs = packer.MultiErrorAppend(
diff --git a/builder/xenserver/xva/builder.go b/builder/xenserver/xva/builder.go
index 00235d2..4eee1c4 100644
--- a/builder/xenserver/xva/builder.go
+++ b/builder/xenserver/xva/builder.go
@@ -38,7 +38,7 @@ func (self *Builder) Prepare(raws ...interface{}) (params []string, warns []stri
 	}, raws...)
 
 	if err != nil {
-		packer.MultiErrorAppend(errs, err)
+		errs = packer.MultiErrorAppend(errs, err)
 	}
 
 	errs = packer.MultiErrorAppend(