diff --git a/plugins/sideload/sideload.go b/plugins/sideload/sideload.go
index 97c76f9..858af9a 100644
--- a/plugins/sideload/sideload.go
+++ b/plugins/sideload/sideload.go
@@ -2,16 +2,23 @@ package sideload
 
 import (
 	"bytes"
-	"embed"
+	"io/fs"
 	"path/filepath"
 
 	"git.foosoft.net/alex/goldsmith"
 )
 
-type Sideload struct {
-	files       []*goldsmith.File
-	fileSystems []embed.FS
-}
+type (
+	Sideload struct {
+		files       []*goldsmith.File
+		fileSystems []sideloadFs
+	}
+
+	sideloadFs interface {
+		fs.ReadDirFS
+		fs.ReadFileFS
+	}
+)
 
 func New() *Sideload {
 	return &Sideload{}
@@ -45,12 +52,15 @@ func (self *Sideload) Files(files ...*goldsmith.File) *Sideload {
 	return self
 }
 
-func (self *Sideload) FileSystems(fileSystems ...embed.FS) *Sideload {
-	self.fileSystems = append(self.fileSystems, fileSystems...)
+func (self *Sideload) FileSystems(fileSystems ...fs.FS) *Sideload {
+	for _, fileSystem := range fileSystems {
+		self.fileSystems = append(self.fileSystems, fileSystem.(sideloadFs))
+	}
+
 	return self
 }
 
-func (self *Sideload) gatherFsFiles(context *goldsmith.Context, fileSystem embed.FS, path string) ([]*goldsmith.File, error) {
+func (self *Sideload) gatherFsFiles(context *goldsmith.Context, fileSystem sideloadFs, path string) ([]*goldsmith.File, error) {
 	entries, err := fileSystem.ReadDir(path)
 	if err != nil {
 		return nil, err
diff --git a/plugins/sideload/sideload_test.go b/plugins/sideload/sideload_test.go
index bbc0fa8..eac1685 100644
--- a/plugins/sideload/sideload_test.go
+++ b/plugins/sideload/sideload_test.go
@@ -1,6 +1,7 @@
 package sideload
 
 import (
+	"io/fs"
 	"testing"
 
 	"embed"
@@ -13,10 +14,15 @@ import (
 var embedFs embed.FS
 
 func Test(self *testing.T) {
+	subFs, err := fs.Sub(embedFs, "testdata/source")
+	if err != nil {
+		panic(err)
+	}
+
 	harness.Validate(
 		self,
 		func(gs *goldsmith.Goldsmith) {
-			gs.Chain(New().FileSystems(embedFs))
+			gs.Chain(New().FileSystems(subFs))
 		},
 	)
 }
diff --git a/plugins/sideload/testdata/reference/1.txt b/plugins/sideload/testdata/reference/1.txt
new file mode 100644
index 0000000..e69de29
diff --git a/plugins/sideload/testdata/reference/child/2.txt b/plugins/sideload/testdata/reference/child/2.txt
new file mode 100644
index 0000000..e69de29