diff --git a/src/components/ProofStepDialog.vue b/src/components/ProofStepDialog.vue
index e43891623ae8292cec4839db8c323c20b629ba93..c8d0a2b81c9b02802d1df37994bbeba849c2d8b1 100644
--- a/src/components/ProofStepDialog.vue
+++ b/src/components/ProofStepDialog.vue
@@ -211,13 +211,13 @@ export default {
       this.standardAnswer = this.standardAnswer.map(answer => ast.astsToString(answer));
 
       // sort the list for comparison
-      this.standardAnswer.sort();
-      this.answers.sort();
+      const standardAnswerSorted = this.standardAnswer.toSorted();
+      const answersSorted = this.answers.toSorted();
 
-      for (let i = 0; i < this.standardAnswer.length; i++) {
-        const output = validator(this.standardAnswer[i], this.answers[i]);
+      for (let i = 0; i < standardAnswerSorted.length; i++) {
+        const output = validator(standardAnswerSorted[i], answersSorted[i]);
         if (!output[0]) {
-          this.errorMsg = "Incorrect answer in statement " + this.answers[i] + output[1];
+          this.errorMsg = "Incorrect answer in statement " + answersSorted[i] + output[1];
           return;
         }
       }