diff --git a/core/mapping/unmarshaler.go b/core/mapping/unmarshaler.go
index 4069492b..b1ea2dbb 100644
--- a/core/mapping/unmarshaler.go
+++ b/core/mapping/unmarshaler.go
@@ -322,12 +322,13 @@ func (u *Unmarshaler) processNamedField(field reflect.StructField, value reflect
 	if err != nil {
 		return err
 	}
-	k := key
+
+	fullName = join(fullName, key)
+	canonicalKey := key
 	if u.opts.canonicalKey != nil {
-		k = u.opts.canonicalKey(key)
+		canonicalKey = u.opts.canonicalKey(key)
 	}
-	fullName = join(fullName, key)
-	mapValue, hasValue := getValue(m, k)
+	mapValue, hasValue := getValue(m, canonicalKey)
 	if hasValue {
 		return u.processNamedFieldWithValue(field, value, mapValue, key, opts, fullName)
 	}
diff --git a/rest/httpx/requests.go b/rest/httpx/requests.go
index c6469bee..61e4a67e 100644
--- a/rest/httpx/requests.go
+++ b/rest/httpx/requests.go
@@ -24,7 +24,8 @@ const (
 var (
 	formUnmarshaler   = mapping.NewUnmarshaler(formKey, mapping.WithStringValues())
 	pathUnmarshaler   = mapping.NewUnmarshaler(pathKey, mapping.WithStringValues())
-	headerUnmarshaler = mapping.NewUnmarshaler(headerKey, mapping.WithStringValues(), mapping.WithCanonicalKeyFunc(textproto.CanonicalMIMEHeaderKey))
+	headerUnmarshaler = mapping.NewUnmarshaler(headerKey, mapping.WithStringValues(),
+		mapping.WithCanonicalKeyFunc(textproto.CanonicalMIMEHeaderKey))
 )
 
 // Parse parses the request.