# M0149

This error means that you supplied an immutable record field (declared without `var`), where a mutable record field (specified with `var`), was expected.

Erroneous code example:

```motoko
{ count = 0 } : { var count : Nat }
```

If you encounter this error, you should probably insert the `var` keyword:

```motoko
{ var count = 1 } : { var count : Nat }
```