Office Settings & Configuration

How to Fix the Word Error: This Is Not a Valid Number

Algirdas Jasaitis Oct 9, 2026 868 views

Question details

The user needs to resolve an issue in Microsoft Word where a "This is not a valid number" prompt appears, preventing them from completing their tasks.

How to Fix the Word Error: 'This Is Not a Valid Number'

Product: Microsoft Word
Device & OS: not provided
Scenario: Opening a document, starting the application, or attempting to change settings such as font size.
Observed behavior: Word displays a recurring "This is not a valid number" error message, which is typically triggered by a damaged document, an unclear command, or a corrupted Normal template.

Before you start

Before attempting any fixes, identify exactly when the error appears (e.g., during startup, while typing, or when changing font sizes) to help determine whether the issue lies with a specific document or the application itself.

Solution 1Recommended

Rename the Corrupted Normal Template

If the error appears immediately when Word starts, your default Normal.dotm template may be corrupted. Renaming it forces Word to generate a fresh, error-free template upon the next launch.

The Normal template stores default formatting, macros, and styles. When it becomes damaged, it can throw invalid command or number errors during startup. Renaming the file acts as a safe reset without deleting the file entirely.

Close Microsoft Word

Ensure that Microsoft Word is completely closed. You may need to check the Task Manager to verify no background Word processes are running.

Open the Templates Folder

Press the Windows Key + R to open the Run dialog box. Type '%appdata%\Microsoft\Templates' and press Enter to open the directory where your templates are stored.

Rename Normal.dotm

Locate the file named 'Normal.dotm' (or simply 'Normal' depending on your view settings). Right-click the file, select Rename, and change it to 'NormalOld.dotm'.

Restart Word

Open Microsoft Word again. The application will automatically create a new Normal template, which should clear the invalid number error.

Hidden Files: If you cannot find the Normal.dotm file, you may need to enable 'Hidden items' from the View tab in Windows File Explorer.

Solution 2

Run the Microsoft Office Repair Tool

If renaming the template does not resolve the issue, the error might stem from corrupted Microsoft Office application files. Running the built-in repair tool can fix these core files.

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Frequently Asked Questions

Why does Word say 'This is not a valid number' when I change the font size?

This usually happens if you manually type a font size that Word doesn't support, accidentally include non-numeric characters (like letters or symbols), or if the document's formatting data is corrupted. Ensure you are entering a standard numeric value between 1 and 1638.

Will renaming the Normal.dotm template delete my saved documents?

No, your saved documents will not be affected at all. Renaming the Normal template only resets your default formatting preferences, recorded macros, and custom styles back to their original factory settings.

What should I do if the error only happens in one specific document?

If the error is isolated to a single file and doesn't happen when you create a new document, the specific file is likely corrupted. Try opening a new blank document and copying the contents of the corrupted file into it, making sure to leave out the final paragraph mark to avoid copying the corruption.

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