diff --git a/starlarktest/starlarktest.go b/starlarktest/starlarktest.go
index 5868ef0..455435e 100644
--- a/starlarktest/starlarktest.go
+++ b/starlarktest/starlarktest.go
@@ -134,5 +134,5 @@ func freeze(thread *starlark.Thread, _ *starlark.Builtin, args starlark.Tuple, k
 // 'go build', under which a test runs in its package directory,
 // and Blaze, under which a test runs in the root of the tree.
 var DataFile = func(pkgdir, filename string) string {
-	return filepath.Join(build.Default.GOPATH, "src/go.starlark.net", pkgdir, filename)
+	return filepath.Join(strings.Split(build.Default.GOPATH, ":")[0], "src/go.starlark.net", pkgdir, filename)
 }