dep ensure --add github.com/remind101/pkg fails with an error

[gitleet]

I get this error:

$ dep ensure --add github.com/remind101/pkg
Fetching sources...

Solving failure: No versions of github.com/remind101/pkg met constraints:
  master: Could not introduce github.com/remind101/pkg@master, as its subpackage github.com/remind101/pkg does not contain usable Go code (*build.NoGoError).. (Package is required by (root).)
  actual-log-levels: Could not introduce github.com/remind101/pkg@actual-log-levels due to multiple problematic subpackages:
  Subpackage github.com/remind101/pkg does not contain usable Go code (*build.NoGoError).. (Package is required by (root).) Subpackage github.com/remind101/pkg/svc is missing. (Package is required by (root).)
  add-client-info: Could not introduce github.com/remind101/pkg@add-client-info due to multiple problematic subpackages:
  Subpackage github.com/remind101/pkg does not contain usable Go code (*build.NoGoError).. (Package is required by (root).) Subpackage github.com/remind101/pkg/svc is missing. (Package is required by (root).)
  bg-test-vendoring: Could not introduce github.com/remind101/pkg@bg-test-vendoring, as its subpackage github.com/remind101/pkg does not contain usable Go code (*build.NoGoError).. (Package is required by (root).)
  dd_apm: Could not introduce github.com/remind101/pkg@dd_apm due to multiple problematic subpackages:
  Subpackage github.com/remind101/pkg does not contain usable Go code (*build.NoGoError).. (Package is required by (root).) Subpackage github.com/remind101/pkg/svc is missing. (Package is required by (root).)
  decouple-svc: Could not introduce github.com/remind101/pkg@decouple-svc, as its subpackage github.com/remind101/pkg does not contain usable Go code (*build.NoGoError).. (Package is required by (root).)

Am I doing something wrong?