diff --git a/torisetsu/src/jsMain/kotlin/core/ComposeQuiz.kt b/torisetsu/src/jsMain/kotlin/core/ComposeQuiz.kt
index ab2e7be..bfe8527 100644
--- a/torisetsu/src/jsMain/kotlin/core/ComposeQuiz.kt
+++ b/torisetsu/src/jsMain/kotlin/core/ComposeQuiz.kt
@@ -45,8 +45,8 @@ class ComposeQuiz : Quiz {
             ),
         ),
     )
-    override var currentQuizId: MutableState<Int> = mutableStateOf(0)
-    override var currentQuizNumber: MutableState<Int> = mutableStateOf(1)
+    override val currentQuizId: MutableState<Int> = mutableStateOf(0)
+    override val currentQuizNumber: MutableState<Int> = mutableStateOf(1)
 
     override fun onClickNext(answerOption: AnswerOption, onClickFinish: (nextId: Int) -> Unit) {
         if (answerOption.isFinish) {
diff --git a/torisetsu/src/jsMain/kotlin/core/Quiz.kt b/torisetsu/src/jsMain/kotlin/core/Quiz.kt
index becb157..82c4451 100644
--- a/torisetsu/src/jsMain/kotlin/core/Quiz.kt
+++ b/torisetsu/src/jsMain/kotlin/core/Quiz.kt
@@ -5,8 +5,8 @@ import androidx.compose.runtime.MutableState
 import data.AnswerOption
 
 interface Quiz {
-    var currentQuizId: MutableState<Int>
-    var currentQuizNumber: MutableState<Int>
+    val currentQuizId: MutableState<Int>
+    val currentQuizNumber: MutableState<Int>
     fun onClickNext(answerOption: AnswerOption, onClickFinish: (nextId: Int) -> Unit)
     fun getAnswerOptions(): List<AnswerOption>
     fun getQuestionText(): String