diff --git a/package-lock.json b/package-lock.json
index e0ac4e728..c454125c5 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -23,7 +23,6 @@
         "@types/mocha": "^9.0.0",
         "@types/node": "^22.19.3",
         "@types/trusted-types": "^1.0.6",
-        "@types/utf8": "^3.0.0",
         "@types/webpack": "^5.28.0",
         "@types/ws": "^8.2.0",
         "@typescript-eslint/eslint-plugin": "^8.50.1",
@@ -47,7 +46,6 @@
         "ts-loader": "^9.3.1",
         "typescript": "^5.9.3",
         "typescript-eslint": "^8.50.1",
-        "utf8": "^3.0.0",
         "webpack": "^5.61.0",
         "webpack-cli": "^4.9.1",
         "ws": "^8.2.3",
@@ -1726,12 +1724,6 @@
       "integrity": "sha512-230RC8sFeHoT6sSUlRO6a8cAnclO06eeiq1QDfiv2FGCLWFvvERWgwIQD4FWqD9A69BN7Lzee4OXwoMVnnsWDw==",
       "dev": true
     },
-    "node_modules/@types/utf8": {
-      "version": "3.0.3",
-      "resolved": "https://registry.npmjs.org/@types/utf8/-/utf8-3.0.3.tgz",
-      "integrity": "sha512-+lqLGxWZsEe4Z6OrzBI7Ym4SMUTaMS5yOrHZ0/IL0bpIye1Qbs4PpobJL2mLDbftUXlPFZR7fu6d1yM+bHLX1w==",
-      "dev": true
-    },
     "node_modules/@types/webpack": {
       "version": "5.28.5",
       "resolved": "https://registry.npmjs.org/@types/webpack/-/webpack-5.28.5.tgz",
@@ -7360,12 +7352,6 @@
         "punycode": "^2.1.0"
       }
     },
-    "node_modules/utf8": {
-      "version": "3.0.0",
-      "resolved": "https://registry.npmjs.org/utf8/-/utf8-3.0.0.tgz",
-      "integrity": "sha512-E8VjFIQ/TyQgp+TZfS6l8yp/xWppSAHzidGiRrqe4bK4XP9pTRyKFgGJpO3SN7zdX4DeomTrwaseCHovfpFcqQ==",
-      "dev": true
-    },
     "node_modules/utils-merge": {
       "version": "1.0.1",
       "resolved": "https://registry.npmjs.org/utils-merge/-/utils-merge-1.0.1.tgz",
diff --git a/package.json b/package.json
index f664f5411..76287f33a 100644
--- a/package.json
+++ b/package.json
@@ -87,7 +87,6 @@
     "@types/mocha": "^9.0.0",
     "@types/node": "^22.19.3",
     "@types/trusted-types": "^1.0.6",
-    "@types/utf8": "^3.0.0",
     "@types/webpack": "^5.28.0",
     "@types/ws": "^8.2.0",
     "@typescript-eslint/eslint-plugin": "^8.50.1",
@@ -111,7 +110,6 @@
     "ts-loader": "^9.3.1",
     "typescript": "^5.9.3",
     "typescript-eslint": "^8.50.1",
-    "utf8": "^3.0.0",
     "webpack": "^5.61.0",
     "webpack-cli": "^4.9.1",
     "ws": "^8.2.3",
diff --git a/src/common/input/TextDecoder.test.ts b/src/common/input/TextDecoder.test.ts
index a0a4a3230..1959e1591 100644
--- a/src/common/input/TextDecoder.test.ts
+++ b/src/common/input/TextDecoder.test.ts
@@ -5,7 +5,6 @@
 
 import { assert } from 'chai';
 import { StringToUtf32, stringFromCodePoint, Utf8ToUtf32, utf32ToString } from 'common/input/TextDecoder';
-import { encode } from 'utf8';
 
 
 // convert UTF32 codepoints to string
@@ -29,6 +28,35 @@ function fromByteString(s: string): Uint8Array {
   return result;
 }
 
+function stringToUtf8Bytes(s: string): Uint8Array {
+  const bytes: number[] = [];
+  for (let i = 0; i < s.length; i++) {
+    let cp = s.charCodeAt(i);
+    if (cp >= 0xD800 && cp <= 0xDBFF && i + 1 < s.length) {
+      const next = s.charCodeAt(i + 1);
+      if (next >= 0xDC00 && next <= 0xDFFF) {
+        cp = 0x10000 + ((cp - 0xD800) << 10) + (next - 0xDC00);
+        i++;
+      }
+    }
+    if (cp < 0x80) {
+      bytes.push(cp);
+    } else if (cp < 0x800) {
+      bytes.push(0xC0 | (cp >> 6), 0x80 | (cp & 0x3F));
+    } else if (cp < 0x10000) {
+      bytes.push(0xE0 | (cp >> 12), 0x80 | ((cp >> 6) & 0x3F), 0x80 | (cp & 0x3F));
+    } else {
+      bytes.push(
+        0xF0 | (cp >> 18),
+        0x80 | ((cp >> 12) & 0x3F),
+        0x80 | ((cp >> 6) & 0x3F),
+        0x80 | (cp & 0x3F)
+      );
+    }
+  }
+  return new Uint8Array(bytes);
+}
+
 function assertDecodedRange(
   min: number,
   max: number,
@@ -172,7 +200,7 @@ describe('text encodings', () => {
             max,
             (i) => (i >= 0xD800 && i <= 0xDFFF) || i === 0xFEFF,
             (i) => String.fromCharCode(i),
-            (input, target) => decoder.decode(fromByteString(encode(input)), target),
+            (input, target) => decoder.decode(stringToUtf8Bytes(input), target),
             (data, length) => toString(data, length)
           );
         });
@@ -187,7 +215,7 @@ describe('text encodings', () => {
             max,
             () => false,
             (i) => stringFromCodePoint(i),
-            (input, target) => decoder.decode(fromByteString(encode(input)), target),
+            (input, target) => decoder.decode(stringToUtf8Bytes(input), target),
             (data, length) => toString(data, length)
           );
         });
@@ -196,7 +224,7 @@ describe('text encodings', () => {
       it('0xFEFF(BOM)', () => {
         const decoder = new Utf8ToUtf32();
         const target = new Uint32Array(5);
-        const utf8Data = fromByteString(encode(String.fromCharCode(0xFEFF)));
+        const utf8Data = stringToUtf8Bytes(String.fromCharCode(0xFEFF));
         const length = decoder.decode(utf8Data, target);
         assert.equal(length, 0);
         decoder.clear();
@@ -207,7 +235,7 @@ describe('text encodings', () => {
       const decoder = new Utf8ToUtf32();
       const target = new Uint32Array(500);
       for (let i = 0; i < TEST_STRINGS.length; ++i) {
-        const utf8Data = fromByteString(encode(TEST_STRINGS[i]));
+        const utf8Data = stringToUtf8Bytes(TEST_STRINGS[i]);
         const length = decoder.decode(utf8Data, target);
         assert.equal(toString(target, length), TEST_STRINGS[i]);
         decoder.clear();