diff --git a/packages/frontend/src/scripts/nyaize.ts b/packages/frontend/src/scripts/nyaize.ts
index abc8ada461..58ed88fed1 100644
--- a/packages/frontend/src/scripts/nyaize.ts
+++ b/packages/frontend/src/scripts/nyaize.ts
@@ -3,21 +3,26 @@
  * SPDX-License-Identifier: AGPL-3.0-only
  */
 
-const enRegex1 = /(?<=n)a/gi;
-const enRegex2 = /(?<=morn)ing/gi;
-const enRegex3 = /(?<=every)one/gi;
 const koRegex1 = /[나-낳]/g;
 const koRegex2 = /(다$)|(다(?=\.))|(다(?= ))|(다(?=!))|(다(?=\?))/gm;
 const koRegex3 = /(야(?=\?))|(야$)|(야(?= ))/gm;
 
+function ifAfter(prefix, fn) {
+	const preLen = prefix.length;
+	const regex = new RegExp(prefix,'i');
+	return (x,pos,string) => {
+		return pos > 0 && string.substring(pos-preLen,pos).match(regex) ? fn(x) : x;
+	};
+}
+
 export function nyaize(text: string): string {
 	return text
 		// ja-JP
 		.replaceAll('な', 'にゃ').replaceAll('ナ', 'ニャ').replaceAll('ﾅ', 'ﾆｬ')
 		// en-US
-		.replace(enRegex1, x => x === 'A' ? 'YA' : 'ya')
-		.replace(enRegex2, x => x === 'ING' ? 'YAN' : 'yan')
-		.replace(enRegex3, x => x === 'ONE' ? 'NYAN' : 'nyan')
+		.replace(/a/gi, ifAfter('n', x => x === 'A' ? 'YA' : 'ya'))
+		.replace(/ing/gi, ifAfter('morn', x => x === 'ING' ? 'YAN' : 'yan'))
+		.replace(/one/gi, ifAfter('every', x => x === 'ONE' ? 'NYAN' : 'nyan'))
 		// ko-KR
 		.replace(koRegex1, match => String.fromCharCode(
 			match.charCodeAt(0)! + '냐'.charCodeAt(0) - '나'.charCodeAt(0),
diff --git a/packages/frontend/test/nyaize.test.ts b/packages/frontend/test/nyaize.test.ts
new file mode 100644
index 0000000000..d4f0fff1db
--- /dev/null
+++ b/packages/frontend/test/nyaize.test.ts
@@ -0,0 +1,32 @@
+import { describe, test, assert, afterEach } from 'vitest';
+import { nyaize } from '@/scripts/nyaize.js';
+
+function runTests(cases) {
+    for (const c of cases) {
+        const [input,expected] = c;
+        const got = nyaize(input);
+        assert.strictEqual(got, expected);
+    }
+}
+
+describe('nyaize', () => {
+    test('ja-JP', () => {
+        runTests([
+            ['きれいな','きれいにゃ'],
+            ['ナナナ', 'ニャニャニャ'],
+            ['ﾅﾅ','ﾆｬﾆｬ'],
+        ]);
+    });
+    test('en-US', () => {
+        runTests([
+            ['bar','bar'],
+            ['banana','banyanya'],
+            ['booting','booting'],
+            ['morning','mornyan'],
+            ['mmmorning','mmmornyan'],
+            ['someone','someone'],
+            ['everyone','everynyan'],
+            ['foreveryone','foreverynyan'],
+        ]);
+    });
+});