diff --git a/os.go b/os.go
index 43fed134..1d0b538d 100644
--- a/os.go
+++ b/os.go
@@ -64,8 +64,8 @@ func MustReadFile(filePath string) []byte {
 	return fileBytes
 }
 
-func WriteFile(filePath string, contents []byte) error {
-	err := ioutil.WriteFile(filePath, contents, 0600)
+func WriteFile(filePath string, contents []byte, mode os.FileMode) error {
+	err := ioutil.WriteFile(filePath, contents, mode)
 	if err != nil {
 		return err
 	}
@@ -73,8 +73,8 @@ func WriteFile(filePath string, contents []byte) error {
 	return nil
 }
 
-func MustWriteFile(filePath string, contents []byte) {
-	err := WriteFile(filePath, contents)
+func MustWriteFile(filePath string, contents []byte, mode os.FileMode) {
+	err := WriteFile(filePath, contents, mode)
 	if err != nil {
 		Exit(Fmt("MustWriteFile failed: %v", err))
 	}
@@ -83,20 +83,20 @@ func MustWriteFile(filePath string, contents []byte) {
 // Writes to newBytes to filePath.
 // Guaranteed not to lose *both* oldBytes and newBytes,
 // (assuming that the OS is perfect)
-func WriteFileAtomic(filePath string, newBytes []byte) error {
+func WriteFileAtomic(filePath string, newBytes []byte, mode os.FileMode) error {
 	// If a file already exists there, copy to filePath+".bak" (overwrite anything)
 	if _, err := os.Stat(filePath); !os.IsNotExist(err) {
 		fileBytes, err := ioutil.ReadFile(filePath)
 		if err != nil {
 			return fmt.Errorf("Could not read file %v. %v", filePath, err)
 		}
-		err = ioutil.WriteFile(filePath+".bak", fileBytes, 0600)
+		err = ioutil.WriteFile(filePath+".bak", fileBytes, mode)
 		if err != nil {
 			return fmt.Errorf("Could not write file %v. %v", filePath+".bak", err)
 		}
 	}
 	// Write newBytes to filePath.new
-	err := ioutil.WriteFile(filePath+".new", newBytes, 0600)
+	err := ioutil.WriteFile(filePath+".new", newBytes, mode)
 	if err != nil {
 		return fmt.Errorf("Could not write file %v. %v", filePath+".new", err)
 	}