diff --git a/chown_linux.go b/chown_linux.go
index 465f569..642eec1 100644
--- a/chown_linux.go
+++ b/chown_linux.go
@@ -9,7 +9,11 @@ import (
 var osChown = os.Chown
 
 func chown(name string, info os.FileInfo) error {
-	f, err := os.OpenFile(name, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, info.Mode())
+	return chownWithMode(name, info, info.Mode())
+}
+
+func chownWithMode(name string, info os.FileInfo, mode os.FileMode) error {
+	f, err := os.OpenFile(name, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, mode)
 	if err != nil {
 		return err
 	}
diff --git a/linux_test.go b/linux_test.go
index d1423c3..3801988 100644
--- a/linux_test.go
+++ b/linux_test.go
@@ -18,7 +18,6 @@ func testMaintainMode(t *testing.T, fileMode fs.FileMode) {
 
 	filename := logFile(dir)
 
-	mode := os.FileMode(0600)
 	l := &Logger{
 		Filename:   filename,
 		MaxBackups: 1,
@@ -27,6 +26,7 @@ func testMaintainMode(t *testing.T, fileMode fs.FileMode) {
 	}
 	defer l.Close()
 
+	mode := defaultFileMode
 	// If custom file mode is set then use it.
 	if l.fileModeIsSet() {
 		mode = l.FileMode
@@ -89,7 +89,7 @@ func TestMaintainOwner(t *testing.T) {
 
 	filename := logFile(dir)
 
-	f, err := os.OpenFile(filename, os.O_CREATE|os.O_RDWR, 0644)
+	f, err := os.OpenFile(filename, os.O_CREATE|os.O_RDWR, defaultFileMode)
 	isNil(err, t)
 	f.Close()
 
@@ -121,7 +121,6 @@ func testCompressMaintainMode(t *testing.T, fileMode fs.FileMode) {
 
 	filename := logFile(dir)
 
-	mode := os.FileMode(0600)
 	l := &Logger{
 		Compress:   true,
 		Filename:   filename,
@@ -131,6 +130,7 @@ func testCompressMaintainMode(t *testing.T, fileMode fs.FileMode) {
 	}
 	defer l.Close()
 
+	mode := defaultFileMode
 	// If custom file mode is set then use it.
 	if l.fileModeIsSet() {
 		mode = l.FileMode
@@ -199,7 +199,7 @@ func TestCompressMaintainOwner(t *testing.T) {
 
 	filename := logFile(dir)
 
-	f, err := os.OpenFile(filename, os.O_CREATE|os.O_RDWR, 0644)
+	f, err := os.OpenFile(filename, os.O_CREATE|os.O_RDWR, defaultFileMode)
 	isNil(err, t)
 	f.Close()
 
@@ -292,3 +292,68 @@ func TestFileModeIsSet(t *testing.T) {
 		equals(c.isSet, l.fileModeIsSet(), t)
 	}
 }
+
+func testChangeModeOnRotate(t *testing.T, oldMode fs.FileMode, newMode fs.FileMode) {
+	currentTime = fakeTime
+	dir := t.TempDir()
+	defer os.RemoveAll(dir)
+
+	// create logger
+	filename := logFile(dir)
+	l := &Logger{
+		Filename:   filename,
+		MaxBackups: 1,
+		MaxSize:    100, // megabytes
+		FileMode:   oldMode,
+	}
+	defer l.Close()
+
+	// create file
+	mode := defaultFileMode
+	if l.fileModeIsSet() {
+		mode = l.FileMode
+	}
+	f, err := os.OpenFile(filename, os.O_CREATE|os.O_RDWR, mode)
+	isNil(err, t)
+	f.Close()
+
+	// change logger file mode
+	l.FileMode = newMode
+
+	// write something to the file
+	b := []byte("boo!")
+	n, err := l.Write(b)
+	isNil(err, t)
+	equals(len(b), n, t)
+
+	// check that file permissions didn't change
+	info, err := os.Stat(filename)
+	isNil(err, t)
+	equals(mode, info.Mode(), t)
+
+	// rotate the file
+	newFakeTime()
+	err = l.Rotate()
+	isNil(err, t)
+
+	// check permissions for the rotated file
+	rotatedFilename := backupFile(dir)
+	rotatedInfo, err := os.Stat(rotatedFilename)
+	isNil(err, t)
+	equals(mode, rotatedInfo.Mode(), t)
+	// check permissions for the new file
+	expected := oldMode
+	if l.fileModeIsSet() {
+		expected = l.FileMode
+	}
+	info, err = os.Stat(filename)
+	isNil(err, t)
+	equals(expected, info.Mode(), t)
+}
+
+func TestChangeModeOnRotate(t *testing.T) {
+	testChangeModeOnRotate(t, 0600, 0644)
+	testChangeModeOnRotate(t, 0644, 0600)
+	testChangeModeOnRotate(t, 0000, 0640)
+	testChangeModeOnRotate(t, 0640, 0000)
+}
diff --git a/lumberjack.go b/lumberjack.go
index 3f86a52..f3f4694 100644
--- a/lumberjack.go
+++ b/lumberjack.go
@@ -132,6 +132,8 @@ var (
 	// variable so tests can mock it out and not need to write megabytes of data
 	// to disk.
 	megabyte = 1024 * 1024
+
+	defaultFileMode = os.FileMode(0644)
 )
 
 // Write implements io.Writer.  If a write would cause the log file to be larger
@@ -218,16 +220,17 @@ func (l *Logger) openNew() error {
 	}
 
 	name := l.filename()
-	mode := os.FileMode(0644)
-
+	mode := defaultFileMode
 	if l.fileModeIsSet() {
 		mode = l.FileMode
 	}
 
 	info, err := osStat(name)
 	if err == nil {
-		// Copy the mode off the old logfile.
-		mode = info.Mode()
+		// If file mode is not set, use the mode of the existing file.
+		if !l.fileModeIsSet() {
+			mode = info.Mode()
+		}
 		// move the existing file
 		newname := backupName(name, l.LocalTime)
 		if err := os.Rename(name, newname); err != nil {
@@ -235,7 +238,7 @@ func (l *Logger) openNew() error {
 		}
 
 		// this is a no-op anywhere but linux
-		if err := chown(name, info); err != nil {
+		if err := chownWithMode(name, info, mode); err != nil {
 			return err
 		}
 	}
@@ -288,7 +291,7 @@ func (l *Logger) openExistingOrNew(writeLen int) error {
 		return l.rotate()
 	}
 
-	file, err := os.OpenFile(filename, os.O_APPEND|os.O_WRONLY, 0644)
+	file, err := os.OpenFile(filename, os.O_APPEND|os.O_WRONLY, defaultFileMode)
 	if err != nil {
 		// if we fail to open the old log file for some reason, just ignore
 		// it and open a new log file.