diff --git a/src/main/java/com/adobe/epubcheck/ocf/OCFChecker.java b/src/main/java/com/adobe/epubcheck/ocf/OCFChecker.java
index 5680a9e58..29fd03960 100755
--- a/src/main/java/com/adobe/epubcheck/ocf/OCFChecker.java
+++ b/src/main/java/com/adobe/epubcheck/ocf/OCFChecker.java
@@ -307,9 +307,11 @@ else if (validationVersion == EPUBVersion.VERSION_3)
     //
     try
     {
+      // report duplicate entries
       Set<String> entriesSet = new HashSet<String>();
       Set<String> normalizedEntriesSet = new HashSet<String>();
-      for (final String entry : ocf.getFileEntries())
+      // run duplicate check from the LinkedList which may contain duplicates
+      for (final String entry : ocf.getEntries())
       {
         if (!entriesSet.add(entry.toLowerCase(Locale.ENGLISH)))
         {
@@ -319,7 +321,11 @@ else if (!normalizedEntriesSet.add(Normalizer.normalize(entry, Form.NFC)))
         {
           report.message(MessageId.OPF_061, EPUBLocation.create(ocf.getPackagePath()), entry);
         }
+      }
 
+      // check all file entries without duplicates
+      for (final String entry : ocf.getFileEntries())
+      {
         ocf.reportMetadata(entry, report);
 
         // if the entry is not in the whitelist (META-INF/* + mimetype)
@@ -345,6 +351,7 @@ public boolean apply(OPFHandler opfHandler)
         OCFFilenameChecker.checkCompatiblyEscaped(entry, report, validationVersion);
       }
 
+      // check all directory entries without duplicates
       for (String directory : ocf.getDirectoryEntries())
       {
         boolean hasContents = false;
diff --git a/src/main/java/com/adobe/epubcheck/ocf/OCFPackage.java b/src/main/java/com/adobe/epubcheck/ocf/OCFPackage.java
index 2b809c2cf..6ee0b189b 100644
--- a/src/main/java/com/adobe/epubcheck/ocf/OCFPackage.java
+++ b/src/main/java/com/adobe/epubcheck/ocf/OCFPackage.java
@@ -107,14 +107,14 @@ public abstract List<String> getEntries()
     throws IOException;
 
   /**
-   * @return a set of relative file names of files in this container
+   * @return a set of relative file names of files in this container (cleaned from duplicates)
    * @throws IOException
    */
   public abstract Set<String> getFileEntries()
     throws IOException;
 
   /**
-   * @return a set of relative directory entries in this container
+   * @return a set of relative directory entries in this container (cleaned from duplicates)
    * @throws IOException
    */
   public abstract Set<String> getDirectoryEntries()
diff --git a/src/main/java/com/adobe/epubcheck/ocf/OCFZipPackage.java b/src/main/java/com/adobe/epubcheck/ocf/OCFZipPackage.java
index 18b609ecf..591d2a488 100644
--- a/src/main/java/com/adobe/epubcheck/ocf/OCFZipPackage.java
+++ b/src/main/java/com/adobe/epubcheck/ocf/OCFZipPackage.java
@@ -6,7 +6,6 @@
 import java.security.MessageDigest;
 import java.util.Collections;
 import java.util.Enumeration;
-import java.util.HashSet;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Set;
@@ -150,16 +149,14 @@ public Set<String> getFileEntries() throws
   public Set<String> getDirectoryEntries() throws
       IOException
   {
-    HashSet<String> entryNames = new HashSet<String>();
-    for (Enumeration<? extends ZipEntry> entries = zip.entries(); entries.hasMoreElements(); )
+    synchronized (zip)
     {
-      ZipEntry entry = entries.nextElement();
-      if (entry.isDirectory())
+      if (allEntries == null)
       {
-        entryNames.add(entry.getName());
+        listEntries();
       }
+      return Collections.unmodifiableSet(dirEntries);
     }
-    return entryNames;
   }
 
   public void reportMetadata(String fileName, Report report)
diff --git a/src/test/java/com/adobe/epubcheck/api/Epub30CheckTest.java b/src/test/java/com/adobe/epubcheck/api/Epub30CheckTest.java
index 7cf1a548b..d8340dd4d 100644
--- a/src/test/java/com/adobe/epubcheck/api/Epub30CheckTest.java
+++ b/src/test/java/com/adobe/epubcheck/api/Epub30CheckTest.java
@@ -208,13 +208,14 @@ public void testFilenameContainsSpacesIssue239()
   public void testDuplicateZipEntriesIssue265()
   {
     // duplicate entries should raise an error
+    Collections.addAll(expectedErrors, MessageId.OPF_060);
     testValidateDocument("invalid/issue265.epub");
   }
 
   @Test
   public void testDuplicateZipEntriesIssue265b()
   {
-    Collections.addAll(expectedWarnings, MessageId.OPF_003, MessageId.PKG_012, MessageId.OPF_061,
+    Collections.addAll(expectedWarnings, MessageId.OPF_061, MessageId.OPF_003, MessageId.PKG_012,
         MessageId.PKG_012);
     // non-unique entry names (after NFC normalization) should raise a warning
     testValidateDocument("invalid/issue265b.epub");