diff --git a/src/explorer/FileNameFormGroup.tsx b/src/explorer/FileNameFormGroup.tsx
index c2154b8b..30f9032d 100644
--- a/src/explorer/FileNameFormGroup.tsx
+++ b/src/explorer/FileNameFormGroup.tsx
@@ -3,15 +3,14 @@
 
 import { Classes, FormGroup, InputGroup, Intent, Tag } from '@blueprintjs/core';
 import { useI18n } from '@shopify/react-i18n';
-import React, { useMemo } from 'react';
-import { FileNameValidationResult, validateFileName } from '../pybricksMicropython/lib';
-import { useSelector } from '../reducers';
+import React from 'react';
+import { FileNameValidationResult } from '../pybricksMicropython/lib';
 import { NewFileWizardStringId } from './i18n';
 import en from './i18n.en.json';
 
 type FileNameHelpTextProps = {
     /** The result of the file name validation. */
-    validation: Exclude<FileNameValidationResult, FileNameValidationResult.Unknown>;
+    validation: FileNameValidationResult;
 };
 
 /**
@@ -81,12 +80,12 @@ type FileNameFormGroupProps = {
     readonly fileName: string;
     /** The file extension (including leading ".") */
     readonly fileExtension: string;
+    /** The result of the file name validation. */
+    readonly validationResult: FileNameValidationResult;
     /** Ref to get handle to input (e.g to be able to call focus()) */
     readonly inputRef?: React.RefObject<HTMLInputElement>;
     /** Called when the user changes the text in the input box. */
     readonly onChange: (newName: string) => void;
-    /** Called when `fileName` is validated. */
-    readonly onValidation: (result: FileNameValidationResult) => void;
 };
 
 /**
@@ -95,30 +94,22 @@ type FileNameFormGroupProps = {
 const FileNameFormGroup: React.VoidFunctionComponent<FileNameFormGroupProps> = ({
     fileName,
     fileExtension,
+    validationResult,
     inputRef,
     onChange,
-    onValidation,
 }) => {
     const [i18n] = useI18n({ id: 'explorer', translations: { en }, fallback: en });
-    const fileNames = useSelector((s) => s.fileStorage.fileNames);
 
-    const [fileNameValidation, fileNameIntent] = useMemo(() => {
-        const result = validateFileName(fileName, fileExtension, fileNames);
-
-        // can't call callback now because it would break react, so defer it
-        setTimeout(() => onValidation(result), 0);
-
-        return [
-            result,
-            result === FileNameValidationResult.IsOk ? Intent.NONE : Intent.DANGER,
-        ];
-    }, [fileName, fileExtension, fileNames]);
+    const fileNameIntent =
+        validationResult === FileNameValidationResult.IsOk
+            ? Intent.NONE
+            : Intent.DANGER;
 
     return (
         <FormGroup
             label={i18n.translate(NewFileWizardStringId.FileNameLabel)}
             intent={fileNameIntent}
-            subLabel={<FileNameHelpText validation={fileNameValidation} />}
+            subLabel={<FileNameHelpText validation={validationResult} />}
         >
             <InputGroup
                 aria-label="File name"
diff --git a/src/explorer/NewFileWizard.tsx b/src/explorer/NewFileWizard.tsx
index 4fa70998..de2e94d0 100644
--- a/src/explorer/NewFileWizard.tsx
+++ b/src/explorer/NewFileWizard.tsx
@@ -15,7 +15,9 @@ import { useDispatch } from 'react-redux';
 import {
     FileNameValidationResult,
     pythonFileExtension,
+    validateFileName,
 } from '../pybricksMicropython/lib';
+import { useSelector } from '../reducers';
 import FileNameFormGroup from './FileNameFormGroup';
 import { Hub, explorerCreateNewFile } from './actions';
 import { NewFileWizardStringId } from './i18n';
@@ -39,8 +41,11 @@ const NewFileWizard: React.VoidFunctionComponent<NewFileWizardProps> = ({
     const dispatch = useDispatch();
 
     const [fileName, setFileName] = useState('');
-    const [fileNameValidation, setFileNameValidation] = useState(
-        FileNameValidationResult.Unknown,
+    const fileNames = useSelector((s) => s.fileStorage.fileNames);
+    const fileNameValidation = validateFileName(
+        fileName,
+        pythonFileExtension,
+        fileNames,
     );
     const [hubType, setHubType] = useState(defaultHub);
 
@@ -59,9 +64,9 @@ const NewFileWizard: React.VoidFunctionComponent<NewFileWizardProps> = ({
                 <FileNameFormGroup
                     fileName={fileName}
                     fileExtension={pythonFileExtension}
+                    validationResult={fileNameValidation}
                     inputRef={fileNameInputRef}
                     onChange={setFileName}
-                    onValidation={setFileNameValidation}
                 />
                 <FormGroup label={i18n.translate(NewFileWizardStringId.SmartHubLabel)}>
                     <RadioGroup
diff --git a/src/explorer/RenameFileDialog.tsx b/src/explorer/RenameFileDialog.tsx
index 5702c813..55225fbf 100644
--- a/src/explorer/RenameFileDialog.tsx
+++ b/src/explorer/RenameFileDialog.tsx
@@ -4,7 +4,8 @@
 import { Button, Classes, Dialog } from '@blueprintjs/core';
 import { useI18n } from '@shopify/react-i18n';
 import React, { useCallback, useRef, useState } from 'react';
-import { FileNameValidationResult } from '../pybricksMicropython/lib';
+import { FileNameValidationResult, validateFileName } from '../pybricksMicropython/lib';
+import { useSelector } from '../reducers';
 import FileNameFormGroup from './FileNameFormGroup';
 import { RenameFileStringId } from './i18n';
 import en from './i18n.en.json';
@@ -31,7 +32,8 @@ const RenameFileDialog: React.VoidFunctionComponent<RenameFileDialogProps> = ({
     const [baseName, extension] = oldName.split(/(\.\w+)$/);
 
     const [newName, setNewName] = useState(baseName);
-    const [result, setResult] = useState(FileNameValidationResult.Unknown);
+    const fileNames = useSelector((s) => s.fileStorage.fileNames);
+    const result = validateFileName(newName, extension, fileNames);
 
     const inputRef = useRef<HTMLInputElement>(null);
 
@@ -61,9 +63,9 @@ const RenameFileDialog: React.VoidFunctionComponent<RenameFileDialogProps> = ({
                     <FileNameFormGroup
                         fileName={newName}
                         fileExtension={extension}
+                        validationResult={result}
                         inputRef={inputRef}
                         onChange={setNewName}
-                        onValidation={setResult}
                     />
                 </div>
                 <div className={Classes.DIALOG_FOOTER}>
diff --git a/src/pybricksMicropython/lib.ts b/src/pybricksMicropython/lib.ts
index 8e51d8bb..47a85fbb 100644
--- a/src/pybricksMicropython/lib.ts
+++ b/src/pybricksMicropython/lib.ts
@@ -12,8 +12,6 @@ export const pythonFileMimeType = 'text/x-python';
 
 /** File name validation results. */
 export enum FileNameValidationResult {
-    /** The result is not yet known. */
-    Unknown,
     /** The file name is acceptable. */
     IsOk,
     /** The file name is an empty string. */
@@ -42,7 +40,7 @@ export function validateFileName(
     fileName: string,
     extension: string,
     existingFiles: ReadonlyArray<string>,
-): Exclude<FileNameValidationResult, FileNameValidationResult.Unknown> {
+): FileNameValidationResult {
     if (existingFiles.includes(`${fileName}${extension}`)) {
         return FileNameValidationResult.AlreadyExists;
     }