diff --git a/query.go b/query.go
index 5d47c79..22cca90 100644
--- a/query.go
+++ b/query.go
@@ -132,6 +132,18 @@ func writeArgumentType(w io.Writer, t reflect.Type, value bool) {
 		return
 	}
 
+	if t.Implements(graphqlTypeInterface) {
+		graphqlType, ok := reflect.Zero(t).Interface().(GraphQLType)
+		if ok {
+			io.WriteString(w, graphqlType.GetGraphQLType())
+			if value {
+				// Value is a required type, so add "!" to the end.
+				io.WriteString(w, "!")
+			}
+			return
+		}
+	}
+
 	switch t.Kind() {
 	case reflect.Slice, reflect.Array:
 		// List. E.g., "[Int]".
@@ -141,9 +153,11 @@ func writeArgumentType(w io.Writer, t reflect.Type, value bool) {
 	default:
 		// Named type. E.g., "Int".
 		name := t.Name()
+
 		if name == "string" { // HACK: Workaround for https://github.com/shurcooL/githubv4/issues/12.
 			name = "ID"
 		}
+
 		io.WriteString(w, name)
 	}
 
@@ -257,6 +271,8 @@ func FieldSafe(valStruct reflect.Value, i int) reflect.Value {
 
 var jsonUnmarshaler = reflect.TypeOf((*json.Unmarshaler)(nil)).Elem()
 
+var graphqlTypeInterface = reflect.TypeOf((*GraphQLType)(nil)).Elem()
+
 func isTrue(s string) bool {
 	b, _ := strconv.ParseBool(s)
 	return b
diff --git a/query_test.go b/query_test.go
index 4e9d72b..56e951d 100644
--- a/query_test.go
+++ b/query_test.go
@@ -5,6 +5,8 @@ import (
 	"net/url"
 	"testing"
 	"time"
+
+	"github.com/google/uuid"
 )
 
 type cachedDirective struct {
@@ -582,14 +584,15 @@ func TestConstructSubscription(t *testing.T) {
 							} `graphql:"users(first:10)"`
 						}
 					} `graphql:"issue(number: $issueNumber)"`
-				} `graphql:"repository(owner: $repositoryOwner, name: $repositoryName)"`
+				} `graphql:"repository(owner: $repositoryOwner, name: $repositoryName, review: $userReview)"`
 			}{},
 			inVariables: map[string]interface{}{
 				"repositoryOwner": String("shurcooL-test"),
 				"repositoryName":  String("test-repo"),
 				"issueNumber":     Int(1),
+				"review":          UserReview{},
 			},
-			want: `subscription SearchRepository($issueNumber:Int!$repositoryName:String!$repositoryOwner:String!){repository(owner: $repositoryOwner, name: $repositoryName){issue(number: $issueNumber){reactionGroups{users(first:10){nodes{login}}}}}}`,
+			want: `subscription SearchRepository($issueNumber:Int!$repositoryName:String!$repositoryOwner:String!$review:user_review!){repository(owner: $repositoryOwner, name: $repositoryName, review: $userReview){issue(number: $issueNumber){reactionGroups{users(first:10){nodes{login}}}}}}`,
 		},
 		// Embedded structs without graphql tag should be inlined in query.
 		{
@@ -683,6 +686,18 @@ func TestQueryArguments(t *testing.T) {
 			in:   map[string]interface{}{"ids": &[]ID{"someID", "anotherID"}},
 			want: `$ids:[ID!]`,
 		},
+		{
+			in: map[string]interface{}{
+				"id":           Uuid(uuid.New()),
+				"id_optional":  &val,
+				"ids":          []Uuid{},
+				"ids_optional": []*Uuid{},
+				"my_uuid":      MyUuid(uuid.New()),
+				"review":       UserReview{},
+				"review_input": UserReviewInput{},
+			},
+			want: `$id:uuid!$id_optional:uuid$ids:[uuid!]!$ids_optional:[uuid]!$my_uuid:my_uuid!$review:user_review!$review_input:user_review_input!`,
+		},
 	}
 	for i, tc := range tests {
 		got := queryArguments(tc.in)
@@ -692,6 +707,27 @@ func TestQueryArguments(t *testing.T) {
 	}
 }
 
+var val Uuid
+
+type Uuid uuid.UUID
+
+func (u Uuid) GetGraphQLType() string { return "uuid" }
+
+type MyUuid Uuid
+
+type UserReview struct {
+	Review String
+	UserID String
+}
+
+type UserReviewInput UserReview
+
+func (u UserReview) GetGraphQLType() string { return "user_review" }
+
+func (u UserReviewInput) GetGraphQLType() string { return "user_review_input" }
+
+func (u MyUuid) GetGraphQLType() string { return "my_uuid" }
+
 // Custom GraphQL types for testing.
 type (
 	// DateTime is an ISO-8601 encoded UTC date.
diff --git a/type.go b/type.go
new file mode 100644
index 0000000..c5e9138
--- /dev/null
+++ b/type.go
@@ -0,0 +1,15 @@
+package graphql
+
+// GraphQLType interface is used to specify the GraphQL type associated
+// with a particular type. If a type implements this interface, the name of
+// the variable used while creating the GraphQL query will be the output of
+// the function defined below.
+//
+// In the current implementation, the GetGraphQLType function is applied to
+// the zero value of the type to get the GraphQL type. So those who are
+// implementing the function should avoid referencing the value of the type
+// inside the function. Further, by this design, the output of the GetGraphQLType
+// function will be a constant.
+type GraphQLType interface {
+	GetGraphQLType() string
+}