# non_constant_map_key

> Details about the non_constant_map_key diagnostic produced by the Dart analyzer.



_The keys in a const map literal must be constant._

## Description

The analyzer produces this diagnostic when a key in a constant map literal
isn't a constant value.

## Example

The following code produces this diagnostic because `a` isn't a constant:

```dart
var a = 'a';
var m = const {[!a!]: 0};
```

## Common fixes

If the map needs to be a constant map, then make the key a constant:

```dart
const a = 'a';
var m = const {a: 0};
```

If the map doesn't need to be a constant map, then remove the `const`
keyword:

```dart
var a = 'a';
var m = {a: 0};
```

