Index: src/org/python/core/packagecache/CachedJarsPackageManager.java
===================================================================
--- src/org/python/core/packagecache/CachedJarsPackageManager.java	(revision 7024)
+++ src/org/python/core/packagecache/CachedJarsPackageManager.java	(working copy)
@@ -397,7 +397,10 @@
             for (Entry<String,String> kv : zipPackages.entrySet()) {
                 String classes = kv.getValue();
                 ostream.writeUTF(kv.getKey());
-                ostream.writeUTF(classes);
+                // Make sure each package is not larger than 64k
+                for (String part : splitString(classes, 65535)) {
+                    ostream.writeUTF(part);
+                }
             }
             ostream.close();
         } catch (IOException ioe) {
@@ -406,6 +409,35 @@
     }
 
     /**
+     * Split up a string into several chunks based on a certain size
+     * 
+     *  The writeCacheFile method will use the writeUTF method on a
+     *  DataOutputStream which only allows writing 64k chunks, so use 
+     *  this utility method to split it up
+     * 
+     * @param str - The string to split up into chunks
+     * @param maxLength - The max size a string should be
+     * @return - An array of strings, each of which will not be larger than maxLength
+     */
+    protected static String[] splitString(String str, int maxLength) {
+        if (str == null) {
+        	return null;
+        }
+
+        int len = str.length();
+        if (len <= maxLength) {
+            return new String[] {str};
+        }
+
+        int chunkCount = (int) Math.ceil((float) len / maxLength);
+        String[] chunks = new String[chunkCount];
+        for (int i = 0; i < chunkCount; i++) {
+            chunks[i] = str.substring(i * maxLength, Math.min(i * maxLength + maxLength, len));
+        }
+        return chunks;
+    }
+
+    /**
      * Initializes cache. Eventually reads back cache index. Index persistent
      * storage is accessed through inOpenIndex().
      */
Index: tests/java/org/python/core/packagecache/CachedJarsOver64kTest.java
===================================================================
--- tests/java/org/python/core/packagecache/CachedJarsOver64kTest.java	(revision 0)
+++ tests/java/org/python/core/packagecache/CachedJarsOver64kTest.java	(revision 0)
@@ -0,0 +1,63 @@
+package org.python.core.packagecache;
+
+import java.io.File;
+
+import org.python.core.PyJavaPackage;
+import org.python.core.PyList;
+import org.python.core.packagecache.CachedJarsPackageManager;
+
+import junit.framework.TestCase;
+
+public class CachedJarsOver64kTest extends TestCase {
+
+    private TestCachePackageManager packageManager = null;
+
+    private File jarFile = null;
+
+    @Override
+    public void setUp() {
+        // Find the jar to use
+        packageManager = new TestCachePackageManager(new File(System
+                                                              .getProperty("java.io.tmpdir")));
+        jarFile = new File(System.getProperty("python.test.source.dir")
+                           + "/org/python/core/packagecache", "vim25.jar");
+    }
+
+    public void testJarOver64k() {
+        assertTrue(jarFile.exists());
+        packageManager.addJarToPackages(jarFile, true);
+        assertFalse(packageManager.failed);
+    }
+
+    private class TestCachePackageManager extends CachedJarsPackageManager {
+
+        public boolean failed;
+
+        public TestCachePackageManager(File cachedir) {
+            if (useCacheDir(cachedir)){
+                initCache();
+            }
+        }
+
+        @Override
+        protected void warning(String msg){
+            if (msg.contains("can't write cache file for")) {
+                failed = true;
+            }
+        }
+
+        @Override
+        public void addDirectory(File dir) {}
+        @Override
+        public void addJar(String jarfile, boolean cache) {}
+        @Override
+        public void addJarDir(String dir, boolean cache) {}
+        @Override
+        public PyList doDir(PyJavaPackage jpkg, boolean instantiate, boolean exclpkgs) {
+            return null;
+        }
+        @Override
+        public Class<?> findClass(String pkg, String name, String reason) { return null; }
+        @Override
+        public boolean packageExists(String pkg, String name) { return false; }
+    }
+}