diff --git a/logback-core/src/main/java/ch/qos/logback/core/OutputStreamAppender.java b/logback-core/src/main/java/ch/qos/logback/core/OutputStreamAppender.java
index 1029dfd980..b7a02feedf 100755
--- a/logback-core/src/main/java/ch/qos/logback/core/OutputStreamAppender.java
+++ b/logback-core/src/main/java/ch/qos/logback/core/OutputStreamAppender.java
@@ -136,7 +136,7 @@ public void stop() {
     protected void closeOutputStream() {
         if (this.outputStream != null) {
             try {
-                // before closing we have to output out layout's footer
+                // before closing we have to output out encooder's footer
                 encoderClose();
                 this.outputStream.close();
                 this.outputStream = null;
@@ -204,6 +204,8 @@ private void writeBytes(byte[] byteArray) throws IOException {
         streamWriteLock.lock();
 
         try {
+            // guard against appender having been stop() in parallel
+            // note that the encoding step is performed outside the protection of the streamWriteLock
             if(isStarted()) {
                 writeByteArrayToOutputStreamWithPossibleFlush(byteArray);
                 updateByteCount(byteArray);