diff --git a/lib/server.js b/lib/server.js
index a9bb5a5..a0d139d 100644
--- a/lib/server.js
+++ b/lib/server.js
@@ -55,7 +55,7 @@ export default function (fastify, { filepath }, done) {
       const baseUrl = new URL(fastify.prefix, fastify.listeningOrigin)
       return reader.getStyle(baseUrl.href)
     } catch (error) {
-      if (isENOENT(error)) {
+      if (isFileNotThereError(error)) {
         throw createError(404, error.message)
       }
       console.error(error)
@@ -72,7 +72,7 @@ export default function (fastify, { filepath }, done) {
       const resource = await reader.getResource(path)
       return sendResource(reply, resource)
     } catch (error) {
-      if (isENOENT(error)) {
+      if (isFileNotThereError(error)) {
         throw createError(404, error.message)
       }
       console.error(error)
@@ -82,14 +82,6 @@ export default function (fastify, { filepath }, done) {
   done()
 }
 
-/**
- * @param {unknown} error
- * @returns {error is Error & { code: 'ENOENT' }}
- */
-function isENOENT(error) {
-  return error instanceof Error && 'code' in error && error.code === 'ENOENT'
-}
-
 class DeferredReader {
   /** @type {Reader | undefined} */
   #reader
@@ -132,11 +124,7 @@ class DeferredReader {
           console.log('Error event watching file:', error)
         })
     } catch (error) {
-      if (
-        error instanceof Error &&
-        'code' in error &&
-        (error.code === 'ENOENT' || error.code === 'EPERM')
-      ) {
+      if (isFileNotThereError(error)) {
         // Ignore: File does not exist yet, but we'll try to open it later
       } else {
         throw error
@@ -202,3 +190,15 @@ class DeferredReader {
 function isWin() {
   return process.platform === 'win32'
 }
+
+/**
+ * @param {unknown} error
+ * @returns {error is Error & { code: 'ENOENT' | 'EPERM' }}
+ */
+function isFileNotThereError(error) {
+  return (
+    error instanceof Error &&
+    'code' in error &&
+    (error.code === 'ENOENT' || error.code === 'EPERM')
+  )
+}