diff --git a/src/options/component/WholeSettings.tsx b/src/options/component/WholeSettings.tsx
index a04186d5..1a1fbae3 100644
--- a/src/options/component/WholeSettings.tsx
+++ b/src/options/component/WholeSettings.tsx
@@ -63,6 +63,9 @@ export const WholeSettings: React.FC<Props> = (props) => {
     return immer(orgSettings, (d) => {
       const errors = [];
       for (const key of Object.keys(d)) {
+        if (!(key in newSettings)) {
+          continue;
+        }
         if (!canReplace(d[key], newSettings[key])) {
           errors.push(`Invalid ${key}`);
         }
diff --git a/src/options/logic/data.ts b/src/options/logic/data.ts
index 58eb5a46..710b071d 100644
--- a/src/options/logic/data.ts
+++ b/src/options/logic/data.ts
@@ -53,7 +53,7 @@ const isShiftJisSoleChar = (byte: number) => {
 
 export const preProcessSettings = (settings: MouseDictionarySettings): MouseDictionarySettings => {
   return immer(settings, (d) => {
-    for (let i = 0; i < d.replaceRules.length; i++) {
+    for (let i = 0; i < d?.replaceRules?.length; i++) {
       d.replaceRules[i].key = i.toString();
     }
   });