diff --git a/benchmark/fs/bench-writeFileSync.js b/benchmark/fs/bench-writeFileSync.js
index 29c16f4aa2a12d..dfa8a19e6f0721 100644
--- a/benchmark/fs/bench-writeFileSync.js
+++ b/benchmark/fs/bench-writeFileSync.js
@@ -7,7 +7,7 @@ tmpdir.refresh();
 
 // Some variants are commented out as they do not show a change and just slow
 const bench = common.createBenchmark(main, {
-  encoding: ['utf8'],
+  encoding: ['utf8', 'UTF8'],
   useFd: ['true', 'false'],
   length: [1024, 102400, 1024 * 1024],
 
diff --git a/lib/fs.js b/lib/fs.js
index 618e48a2b892be..2384a5202e5f42 100644
--- a/lib/fs.js
+++ b/lib/fs.js
@@ -92,6 +92,7 @@ const {
     custom: kCustomPromisifiedSymbol,
   },
   SideEffectFreeRegExpPrototypeExec,
+  normalizeEncoding,
   defineLazyProperties,
   isWindows,
   isMacOS,
@@ -428,7 +429,7 @@ function tryReadSync(fd, isUserFd, buffer, pos, len) {
 function readFileSync(path, options) {
   options = getOptions(options, { flag: 'r' });
 
-  if (options.encoding === 'utf8' || options.encoding === 'utf-8') {
+  if (options.encoding && normalizeEncoding(options.encoding) === 'utf8') {
     if (!isInt32(path)) {
       path = getValidatedPath(path);
     }
@@ -2383,7 +2384,7 @@ function writeFileSync(path, data, options) {
   const flag = options.flag || 'w';
 
   // C++ fast path for string data and UTF8 encoding
-  if (typeof data === 'string' && (options.encoding === 'utf8' || options.encoding === 'utf-8')) {
+  if (typeof data === 'string' && normalizeEncoding(options.encoding) === 'utf8') {
     if (!isInt32(path)) {
       path = getValidatedPath(path);
     }