diff --git a/src/core/package.go b/src/core/package.go
index 3786586e93..93c9a85c6c 100644
--- a/src/core/package.go
+++ b/src/core/package.go
@@ -67,15 +67,6 @@ func (pkg *Package) TargetOrDie(name string) *BuildTarget {
 	return t
 }
 
-// SourceRoot returns the root directory of source files for this package.
-// This is equivalent to .Name for in-repo packages but differs for those in subrepos.
-func (pkg *Package) SourceRoot() string {
-	if pkg.Subrepo != nil {
-		return pkg.Subrepo.Dir(pkg.Name)
-	}
-	return pkg.Name
-}
-
 // AddTarget adds a new target to this package with the given name.
 // It doesn't check for duplicates.
 func (pkg *Package) AddTarget(target *BuildTarget) {
diff --git a/src/core/state.go b/src/core/state.go
index 71367d139a..3f9490eb56 100644
--- a/src/core/state.go
+++ b/src/core/state.go
@@ -255,8 +255,7 @@ func (state *BuildState) Initialise(subrepo *Subrepo) (err error) {
 		// handled for us already in plz.go
 		if state.CurrentSubrepo != "" {
 			state.RepoConfig = &Configuration{}
-			err = readConfigFilesInto(state.RepoConfig, append(subrepo.AdditionalConfigFiles, filepath.Join(subrepo.Root, ".plzconfig")))
-			if err != nil {
+			if err := readSubrepoConfig(state.RepoConfig, subrepo); err != nil {
 				return
 			}
 			if err = validateSubrepoNameAndPluginConfig(state.Config, state.RepoConfig, subrepo); err != nil {
diff --git a/src/core/subrepo.go b/src/core/subrepo.go
index bd5831239f..3bb4445a97 100644
--- a/src/core/subrepo.go
+++ b/src/core/subrepo.go
@@ -36,10 +36,15 @@ type Subrepo struct {
 }
 
 func NewSubrepo(state *BuildState, name, root string, target *BuildTarget, arch cli.Arch, isCrosscompile bool) *Subrepo {
+	subrepoFS := os.DirFS(root)
+	if root == "" {
+		// This happens for architecture subrepos, which should use the same FS as the host repo
+		subrepoFS = fs.HostFS
+	}
 	return &Subrepo{
 		Name:           name,
 		Root:           root,
-		FS:             os.DirFS(root),
+		FS:             subrepoFS,
 		State:          state,
 		Target:         target,
 		Arch:           arch,
@@ -81,14 +86,14 @@ func (s *Subrepo) Dir(dir string) string {
 	return filepath.Join(s.Root, dir)
 }
 
-func readConfigFilesInto(repoConfig *Configuration, files []string) error {
-	for _, file := range files {
+func readSubrepoConfig(repoConfig *Configuration, subrepo *Subrepo) error {
+	for _, file := range subrepo.AdditionalConfigFiles {
 		err := readConfigFile(fs.HostFS, repoConfig, file, true)
 		if err != nil {
 			return err
 		}
 	}
-	return nil
+	return readConfigFile(subrepo.FS, repoConfig, ".plzconfig", true)
 }
 
 func validateSubrepoNameAndPluginConfig(config, repoConfig *Configuration, subrepo *Subrepo) error {
diff --git a/src/parse/asp/builtins.go b/src/parse/asp/builtins.go
index b31e43c5db..f33b715710 100644
--- a/src/parse/asp/builtins.go
+++ b/src/parse/asp/builtins.go
@@ -607,10 +607,14 @@ func glob(s *scope, args []pyObject) pyObject {
 	allowEmpty := args[4].IsTruthy()
 	exclude = append(exclude, s.state.Config.Parse.BuildFileName...)
 	if s.globber == nil {
-		s.globber = fs.NewGlobber(fs.HostFS, s.state.Config.Parse.BuildFileName)
+		if s.pkg.Subrepo != nil {
+			s.globber = fs.NewGlobber(s.pkg.Subrepo.FS, s.state.Config.Parse.BuildFileName)
+		} else {
+			s.globber = fs.NewGlobber(fs.HostFS, s.state.Config.Parse.BuildFileName)
+		}
 	}
 
-	glob := s.globber.Glob(s.pkg.SourceRoot(), include, exclude, hidden, includeSymlinks)
+	glob := s.globber.Glob(s.pkg.Name, include, exclude, hidden, includeSymlinks)
 	if !allowEmpty && len(glob) == 0 {
 		// Strip build file name from exclude list for error message
 		exclude = exclude[:len(exclude)-len(s.state.Config.Parse.BuildFileName)]