Link to the code that reproduces this issue

https://github.com/jonasvle/font-reproduction/blob/master/src/app/globals.css

To Reproduce

Define a localFont with custom 'font-family' via declarations.
e.g.

const block_berthold = localFont({
  src: '../app/fonts/BlockBerthold-Condensed.ttf',
  declarations: [
    {
      prop: 'font-family',
      value: 'Block Berthold',
    },
  ],
});

Current vs. Expected behavior

I expect to be able to use the font via font-family: 'Block Berthold', but I can only use it via font-family: 'block_berthold'.

Provide environment information

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 11 Pro
  Available memory (MB): 32421
  Available CPU cores: 20
Binaries:
  Node: 20.14.0
  npm: 10.7.0
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  next: 15.1.6 // Latest available version is detected (15.1.6).
  eslint-config-next: 15.1.6
  react: 19.0.0
  react-dom: 19.0.0
  typescript: 5.7.2
Next.js Config:
  output: standalone

Which area(s) are affected? (Select all that apply)

Font (next/font)

Which stage(s) are affected? (Select all that apply)

next dev (local), next build (local), next start (local), Other (Deployed)

Additional context

No response