diff --git a/godoc/util/util.go b/godoc/util/util.go
index b3eac39a..8e37defa 100644
--- a/godoc/util/util.go
+++ b/godoc/util/util.go
@@ -6,7 +6,6 @@
 package util
 
 import (
-	"io"
 	pathpkg "path"
 	"sync"
 	"time"
@@ -62,11 +61,6 @@ var textExt = map[string]bool{
 	".js":  false, // must be served raw
 }
 
-// FileSystem is a minimal virtual filesystem.
-type FileSystem interface {
-	Open(name string) (io.ReadCloser, error)
-}
-
 // IsTextFile returns whether the file has a known extension indicating
 // a text file, or if a significant chunk of the specified file looks like
 // correct UTF-8; that is, if it is likely that the file contains human-