diff --git a/src/pkg/os/file.go b/src/pkg/os/file.go
index 2dd1fcf282..18cd61d3a8 100644
--- a/src/pkg/os/file.go
+++ b/src/pkg/os/file.go
@@ -140,6 +140,9 @@ func (f *File) Write(b []byte) (n int, err error) {
 	if n < 0 {
 		n = 0
 	}
+	if n != len(b) {
+		err = io.ErrShortWrite
+	}
 
 	epipecheck(f, e)
 
diff --git a/src/pkg/os/file_plan9.go b/src/pkg/os/file_plan9.go
index 708163ee1c..278fae772c 100644
--- a/src/pkg/os/file_plan9.go
+++ b/src/pkg/os/file_plan9.go
@@ -313,8 +313,7 @@ func Remove(name string) error {
 	return nil
 }
 
-// Rename renames a file.
-func Rename(oldname, newname string) error {
+func rename(oldname, newname string) error {
 	var d syscall.Dir
 
 	d.Null()
diff --git a/src/pkg/os/file_posix.go b/src/pkg/os/file_posix.go
index a8bef359b9..90838682b6 100644
--- a/src/pkg/os/file_posix.go
+++ b/src/pkg/os/file_posix.go
@@ -48,8 +48,7 @@ func Readlink(name string) (string, error) {
 	}
 }
 
-// Rename renames a file.
-func Rename(oldname, newname string) error {
+func rename(oldname, newname string) error {
 	e := syscall.Rename(oldname, newname)
 	if e != nil {
 		return &LinkError{"rename", oldname, newname, e}