diff --git a/lists.go b/lists.go
index fd68874..b8e4dcf 100644
--- a/lists.go
+++ b/lists.go
@@ -533,6 +533,15 @@ type MergeFieldsParams struct {
 	Required bool   `json:"required"`
 }
 
+func (p MergeFieldsParams) Params() map[string]string {
+	m := p.ExtendedQueryParams.Params()
+	m["type"] = p.Type
+	if p.Required {
+		m["required"] = "1"
+	}
+	return m
+}
+
 type MergeFieldParams struct {
 	BasicQueryParams