denoland/deno · critical · std::io::Error

Unknown media type value: {value}

Error message

Unknown media type value: {value}

What it means

Compiled Deno binaries embed a metadata section where each specifier's media type is stored as a small integer tag (currently 0–20: Unknown through the newest types). While deserializing, any value outside the known range yields io::ErrorKind::InvalidData 'Unknown media type value: N'. In practice this means the binary's metadata was written by a newer Deno than the runtime reading it (new media types get new tags), or the bytes are corrupted.

Source

Thrown at cli/lib/standalone/binary.rs:307

      4 => MediaType::TypeScript,
      5 => MediaType::Mts,
      6 => MediaType::Cts,
      7 => MediaType::Dts,
      8 => MediaType::Dmts,
      9 => MediaType::Dcts,
      10 => MediaType::Tsx,
      11 => MediaType::Json,
      12 => MediaType::Jsonc,
      13 => MediaType::Json5,
      14 => MediaType::Markdown,
      15 => MediaType::Wasm,
      16 => MediaType::Css,
      17 => MediaType::Html,
      18 => MediaType::SourceMap,
      19 => MediaType::Sql,
      20 => MediaType::Unknown,
      value => {
        return Err(std::io::Error::new(
          std::io::ErrorKind::InvalidData,
          format!("Unknown media type value: {value}"),
        ));
      }
    };
    Ok((input, value))
  }
}

/// Data stored keyed by specifier.
pub struct SpecifierDataStore<TData> {
  data: IndexMap<SpecifierId, TData>,
}

impl<TData> Default for SpecifierDataStore<TData> {
  fn default() -> Self {
    Self {
      data: IndexMap::new(),

View on GitHub (pinned to 9ad36f7a2c)

Solutions

1. Recompile the binary with the same Deno version that will run it (check `deno --version` on both ends)
2. Upgrade the runtime side to at least the version that produced the binary
3. If versions already match, treat the artifact as corrupted: rebuild and verify checksums

Example fix

# before
# built with deno canary 2.x, run on older denort
deno compile -o app src/mod.ts  # on machine A (new)
./app                          # on machine B (old) -> Unknown media type value: 19

# after
# machine B: upgrade, then rebuild there
deno upgrade && deno compile -o app src/mod.ts && ./app

// Stamp the builder version into the artifact and check before running
const BUILT_WITH = "2.4.7"; // set by your build script
if (BUILT_WITH !== Deno.version.deno) {
  throw new Error(`Binary built with deno ${BUILT_WITH} but running under ${Deno.version.deno}; upgrade or rebuild`);
}

// Wrapper that executes a compiled binary
const { code, stderr } = await Deno.command(binary).output();
if (code !== 0 && new TextDecoder().decode(stderr).includes("Unknown media type value")) {
  // forward-incompatible binary: upgrade denort/deno, then re-run
}

When it happens

Trigger: Running a compiled binary whose embedded data is read by an older deno/denort (forward incompatibility: tag 19 Sql or later added values vs an older reader); offsets into the metadata section shifted by corruption so a non-tag byte is decoded as the tag.

Common situations: Compiling with a new Deno version but executing through an older cached denort or an older wrapper that re-reads the section; artifacts built on a dev machine with Deno canary, deployed to machines with stable Deno; bit-rot in transferred artifacts (usually accompanied by other parse errors).

Related errors

• Unexpected end of data
• unsupported media type {} for {}
• Unexpected end of data
• Unexpected second argument to Deno.bench()
• Unexpected 'fn' field in options, bench function is already

AI-assisted analysis of denoland/deno@9ad36f7a2c (2026-08-20). Data as JSON: /api/errors/befeffb90b51e359. Report an issue: GitHub.