diff --git a/slices/map.go b/slices/map.go
index 7f04eeeed..b395c45cd 100644
--- a/slices/map.go
+++ b/slices/map.go
@@ -47,17 +47,17 @@ func (m Map) Value() (driver.Value, error) {
 
 // UnmarshalJSON will unmarshall JSON value into
 // the map representation of this value.
-func (m Map) UnmarshalJSON(b []byte) error {
+func (m *Map) UnmarshalJSON(b []byte) error {
 	var stuff map[string]interface{}
 	err := json.Unmarshal(b, &stuff)
 	if err != nil {
 		return err
 	}
-	if m == nil {
-		m = Map{}
+	if *m == nil {
+		*m = Map{}
 	}
 	for key, value := range stuff {
-		m[key] = value
+		(*m)[key] = value
 	}
 	return nil
 }