diff --git a/ext/java/org/jruby/ext/digest/RubyDigest.java b/ext/java/org/jruby/ext/digest/RubyDigest.java
index f10b8ca..2af6b5a 100644
--- a/ext/java/org/jruby/ext/digest/RubyDigest.java
+++ b/ext/java/org/jruby/ext/digest/RubyDigest.java
@@ -364,6 +364,8 @@ public static IRubyObject length(ThreadContext context, IRubyObject self) {
 
     @JRubyClass(name="Digest::Class")
     public static class DigestClass extends RubyObject {
+        private static final long serialVersionUID = 1956465293454003972L;
+
         public DigestClass(Ruby runtime, RubyClass type) {
             super(runtime, type);
         }
@@ -397,7 +399,9 @@ public static RubyString bubblebabble(IRubyObject recv, IRubyObject arg) {
 
     @JRubyClass(name="Digest::Base")
     public static class DigestBase extends RubyObject {
-        private MessageDigest algo;
+        private static final long serialVersionUID = -2526926208784906213L;
+
+        private transient MessageDigest algo;
         private int blockLength = 0;
 
         public DigestBase(Ruby runtime, RubyClass type) {