diff --git a/binding/form.go b/binding/form.go
index eef0cc13..09087ae0 100644
--- a/binding/form.go
+++ b/binding/form.go
@@ -66,6 +66,8 @@ func (formMultipartBinding) Bind(req *http.Request, obj interface{}) error {
 
 type multipartRequest http.Request
 
+var _ setter = (*multipartRequest)(nil)
+
 var (
 	multipartFileHeaderStructType = reflect.TypeOf(multipart.FileHeader{})
 )
diff --git a/binding/form_mapping.go b/binding/form_mapping.go
index 85eb4ce5..615e89ff 100644
--- a/binding/form_mapping.go
+++ b/binding/form_mapping.go
@@ -31,12 +31,15 @@ func mapFormByTag(ptr interface{}, form map[string][]string, tag string) error {
 	return mappingByPtr(ptr, formSource(form), tag)
 }
 
+// setter - try to set value on a walking by fields of a struct
 type setter interface {
 	Set(value reflect.Value, field reflect.StructField, key string, opt setOptions) (isSetted bool, err error)
 }
 
 type formSource map[string][]string
 
+var _ setter = formSource(nil)
+
 func (form formSource) Set(value reflect.Value, field reflect.StructField, tagValue string, opt setOptions) (isSetted bool, err error) {
 	return setByForm(value, field, form, tagValue, opt)
 }