golang/go · error · module.VersionError

parsing go.mod: missing module line

Error message

parsing go.mod: missing module line

What it means

When the go command fetches and summarizes a module's go.mod, it expects a `module` declaration giving the module path. If that line is missing (summary.module.Path == "") and the module is NOT a local filesystem replacement (which are exempt), it returns this error wrapped in module.VersionError.

Source

Thrown at src/cmd/go/internal/modload/modfile.go:626

			suggestion := fmt.Sprintf(" for go.mod file; to add it:\n\tgo mod download %s", m.Path)
			return nil, module.VersionError(actual, &sumMissingError{suggestion: suggestion})
		}
	}
	summary, err := rawGoModSummary(ld, actual)
	if err != nil {
		return nil, err
	}

	if actual.Version == "" {
		// The actual module is a filesystem-local replacement, for which we have
		// unfortunately not enforced any sort of invariants about module lines or
		// matching module paths. Anything goes.
		//
		// TODO(bcmills): Remove this special-case, update tests, and add a
		// release note.
	} else {
		if summary.module.Path == "" {
			return nil, module.VersionError(actual, errors.New("parsing go.mod: missing module line"))
		}

		// In theory we should only allow mpath to be unequal to m.Path here if the
		// version that we fetched lacks an explicit go.mod file: if the go.mod file
		// is explicit, then it should match exactly (to ensure that imports of other
		// packages within the module are interpreted correctly). Unfortunately, we
		// can't determine that information from the module proxy protocol: we'll have
		// to leave that validation for when we load actual packages from within the
		// module.
		if mpath := summary.module.Path; mpath != m.Path && mpath != actual.Path {
			return nil, module.VersionError(actual,
				fmt.Errorf("parsing go.mod:\n"+
					"\tmodule declares its path as: %s\n"+
					"\t        but was required as: %s", mpath, m.Path))
		}
	}

	for _, mainModule := range ld.MainModules.Versions() {

View on GitHub (pinned to b6b368adc5)

Solutions

1. Report the issue to the module maintainer to add a module line.
2. Select a different (correct) version of the module.
3. Replace the broken module with a fixed fork via a `replace` directive.

Example fix

// before
// upstream go.mod (broken): no `module` line
$ go get example.com/lib@v1.0.0   // parsing go.mod: missing module line

// after
// replace example.com/lib v1.0.0 => github.com/you/lib-fork v1.0.1

// Before depending on a module, fetch its go.mod summary and check for a module line.
func hasModuleLine(modPath, version string) error {
    return exec.Command("go", "mod", "download", "-json", modPath+"@"+version).Run()
}

null

null

When it happens

Trigger: A version of a module whose published go.mod lacks a `module` line, fetched from a proxy or VCS (actual.Version != "").

Common situations: Hand-edited or corrupt go.mod published by a dependency; ancient pre-modules code; proxy serving truncated content.

Related errors

• ${GoModToolVersion} is required for tool directives in go.mo
• updates to go.mod needed, but go.mod is part of the overlay
• can't resolve module using the vendor directory (Use -mod=m
• not a known dependency
• cannot find package

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/490565b964c17ac2. Report an issue: GitHub.