diff --git a/lang/src/main/java/org/apache/shiro/lang/io/DefaultSerializer.java b/lang/src/main/java/org/apache/shiro/lang/io/DefaultSerializer.java
index 03d06c6acc..a48a176cae 100644
--- a/lang/src/main/java/org/apache/shiro/lang/io/DefaultSerializer.java
+++ b/lang/src/main/java/org/apache/shiro/lang/io/DefaultSerializer.java
@@ -47,6 +47,7 @@ public byte[] serialize(T o) throws SerializationException {
             ObjectOutputStream oos = new ObjectOutputStream(bos);
             oos.writeObject(o);
             oos.close();
+            baos.flush();
             return baos.toByteArray();
         } catch (IOException e) {
             String msg = "Unable to serialize object [" + o + "].  " +