diff --git a/internal/testing/util_test.go b/internal/testing/util_test.go
index a4f03ef..5cede6d 100644
--- a/internal/testing/util_test.go
+++ b/internal/testing/util_test.go
@@ -1,36 +1,42 @@
 package testing
 
 import (
+	"reflect"
 	"testing"
 
 	"gerrit.mcp.mirantis.net/debian/gophercloud.git/internal"
-	th "gerrit.mcp.mirantis.net/debian/gophercloud.git/testhelper"
 )
 
 func TestRemainingKeys(t *testing.T) {
 	type User struct {
-		FirstName string `json:"first_name"`
-		LastName  string `json:"last_name"`
-		City      string
+		UserID    string `json:"user_id"`
+		Username  string `json:"username"`
+		Location  string `json:"-"`
+		CreatedAt string `json:"-"`
+		Status    string
+		IsAdmin   bool
 	}
 
-	userStruct := User{
-		FirstName: "John",
-		LastName:  "Doe",
-	}
-
-	userMap := map[string]interface{}{
-		"first_name": "John",
-		"last_name":  "Doe",
-		"city":       "Honolulu",
-		"state":      "Hawaii",
+	userResponse := map[string]interface{}{
+		"user_id":      "abcd1234",
+		"username":     "jdoe",
+		"location":     "Hawaii",
+		"created_at":   "2017-06-08T02:49:03.000000",
+		"status":       "active",
+		"is_admin":     "true",
+		"custom_field": "foo",
 	}
 
 	expected := map[string]interface{}{
-		"city":  "Honolulu",
-		"state": "Hawaii",
+		"created_at":   "2017-06-08T02:49:03.000000",
+		"is_admin":     "true",
+		"custom_field": "foo",
 	}
 
-	actual := internal.RemainingKeys(userStruct, userMap)
-	th.AssertDeepEquals(t, expected, actual)
+	actual := internal.RemainingKeys(User{}, userResponse)
+
+	isEqual := reflect.DeepEqual(expected, actual)
+	if !isEqual {
+		t.Fatalf("expected %s but got %s", expected, actual)
+	}
 }
diff --git a/internal/util.go b/internal/util.go
index f7e10d2..8efb283 100644
--- a/internal/util.go
+++ b/internal/util.go
@@ -2,23 +2,31 @@
 
 import (
 	"reflect"
+	"strings"
 )
 
-// RemainingKeys will inspect a struct and compare it to a map. Any key that
-// is not defined in a JSON tag of the struct will be added to the extras map
-// and returned.
+// RemainingKeys will inspect a struct and compare it to a map. Any struct
+// field that does not have a JSON tag that matches a key in the map or
+// a matching lower-case field in the map will be returned as an extra.
 //
 // This is useful for determining the extra fields returned in response bodies
 // for resources that can contain an arbitrary or dynamic number of fields.
 func RemainingKeys(s interface{}, m map[string]interface{}) (extras map[string]interface{}) {
 	extras = make(map[string]interface{})
+	for k, v := range m {
+		extras[k] = v
+	}
+
 	valueOf := reflect.ValueOf(s)
 	typeOf := reflect.TypeOf(s)
 	for i := 0; i < valueOf.NumField(); i++ {
 		field := typeOf.Field(i)
-		tagValue := field.Tag.Get("json")
-		if _, ok := m[tagValue]; !ok {
-			extras[tagValue] = m[tagValue]
+
+		lowerField := strings.ToLower(field.Name)
+		delete(extras, lowerField)
+
+		if tagValue := field.Tag.Get("json"); tagValue != "" && tagValue != "-" {
+			delete(extras, tagValue)
 		}
 	}