directory %s is not a package listed in vendor/modules.txt

Error message

directory %s is not a package listed in vendor/modules.txt

What it means

Thrown by resolveLocalPackage (load.go:617) when the directory is inside vendor/ AND -mod=vendor is active, but the package (the suffix after 'vendor/') is not listed in vendor/modules.txt. After confirming vendor mode, the code calls readVendorList and checks vendorPkgModule[pkg]. If the package is not registered in the vendor manifest, the directory is not a recognized vendored package.

Source

Thrown at src/cmd/go/internal/modload/load.go:617

	}

	// Note: The checks for @ here are just to avoid misinterpreting
	// the module cache directories (formerly GOPATH/src/mod/foo@v1.5.2/bar).
	// It's not strictly necessary but helpful to keep the checks.
	var pkgNotFoundErr error
	pkgNotFoundLongestPrefix := ""
	for _, mainModule := range ld.MainModules.Versions() {
		modRoot := ld.MainModules.ModRoot(mainModule)
		if modRoot != "" && str.HasFilePathPrefix(absDir, modRoot) && !strings.Contains(absDir[len(modRoot):], "@") {
			suffix := filepath.ToSlash(str.TrimFilePathPrefix(absDir, modRoot))
			if pkg, found := strings.CutPrefix(suffix, "vendor/"); found {
				if cfg.BuildMod != "vendor" {
					return "", fmt.Errorf("without -mod=vendor, directory %s has no package path", absDir)
				}

				readVendorList(VendorDir(ld))
				if _, ok := vendorPkgModule[pkg]; !ok {
					return "", fmt.Errorf("directory %s is not a package listed in vendor/modules.txt", absDir)
				}
				return pkg, nil
			}

			mainModulePrefix := ld.MainModules.PathPrefix(mainModule)
			if mainModulePrefix == "" {
				pkg := suffix
				if pkg == "builtin" {
					// "builtin" is a pseudo-package with a real source file.
					// It's not included in "std", so it shouldn't resolve from "."
					// within module "std" either.
					return "", errPkgIsBuiltin
				}
				return pkg, nil
			}

			pkg := pathpkg.Join(mainModulePrefix, suffix)
			if _, ok, err := dirInModule(pkg, mainModulePrefix, modRoot, true); err != nil {

View on GitHub (pinned to b6b368adc5)

Solutions

Regenerate the vendor directory and its manifest: run 'go mod vendor'.
Remove any manually-added directories under vendor/ that are not real vendored dependencies.
Ensure the package you are referencing is an actual dependency in go.mod before vendoring.

Example fix

# before — stale vendor manifest
# (vendor/modules.txt missing a package that exists in vendor/)

go build -mod=vendor ./vendor/example.com/newpkg
# error

# after — regenerate vendor tree
go mod vendor
go build -mod=vendor ./...

Defensive patterns

Strategy: validation

Prevention

Run 'go mod vendor' whenever go.mod requirements change to keep vendor/modules.txt in sync.
Never manually add directories under vendor/ — always go through the module system.
If you see unexpected vendor entries, delete vendor/ and regenerate with 'go mod vendor'.

When it happens

Trigger: The vendor/ directory contains a package subdirectory that was added manually or is stale, but vendor/modules.txt does not list it. This happens when -mod=vendor is set and the user points at a vendor subpath not tracked by 'go mod vendor'.

Common situations: Manually copying a package into vendor/ without updating modules.txt. A stale vendor/ directory after go.mod requirements changed but 'go mod vendor' was not re-run. Third-party files dropped into vendor/.

Related errors

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/9e62f2db0edf3e57. Report an issue: GitHub.