diff --git a/src/com/bytezone/diskbrowser/prodos/write/FileAlreadyExistsException.java b/src/com/bytezone/diskbrowser/prodos/write/FileAlreadyExistsException.java
new file mode 100644
index 0000000..4f53b98
--- /dev/null
+++ b/src/com/bytezone/diskbrowser/prodos/write/FileAlreadyExistsException.java
@@ -0,0 +1,9 @@
+package com.bytezone.diskbrowser.prodos.write;
+
+public class FileAlreadyExistsException extends Exception
+{
+  public FileAlreadyExistsException (String message)
+  {
+    super (message);
+  }
+}
diff --git a/src/com/bytezone/diskbrowser/prodos/write/ProdosDisk.java b/src/com/bytezone/diskbrowser/prodos/write/ProdosDisk.java
index 314b193..8c1eee8 100644
--- a/src/com/bytezone/diskbrowser/prodos/write/ProdosDisk.java
+++ b/src/com/bytezone/diskbrowser/prodos/write/ProdosDisk.java
@@ -122,8 +122,8 @@ public class ProdosDisk
 
   // ---------------------------------------------------------------------------------//
   public FileEntry addFile (String path, byte type, int auxType, LocalDateTime created,
-      LocalDateTime modified, byte[] dataBuffer)
-      throws DiskFullException, VolumeCatalogFullException
+      LocalDateTime modified, byte[] fileBuffer, int eof)
+      throws DiskFullException, VolumeCatalogFullException, FileAlreadyExistsException
   // ---------------------------------------------------------------------------------//
   {
     if (path.isBlank ())
@@ -170,7 +170,7 @@ public class ProdosDisk
     {
       System.out.println ("File already exists: " + path);
       System.out.println (fileEntryOpt.get ());
-      return null;          // throw something?
+      throw new FileAlreadyExistsException (fileName);
     }
 
     // create a file entry in the current catalog block
@@ -188,7 +188,7 @@ public class ProdosDisk
       fileEntry.modifiedDate = modified;
 
       FileWriter fileWriter = new FileWriter (this);
-      fileWriter.writeFile (dataBuffer, dataBuffer.length);
+      fileWriter.writeFile (fileBuffer, eof);
 
       fileEntry.storageType = fileWriter.storageType;
       fileEntry.keyPointer = fileWriter.keyPointer;
@@ -197,22 +197,20 @@ public class ProdosDisk
 
       fileEntry.write ();
       updateFileCount (fileEntry.headerPointer);
-
-      return fileEntry;
     }
 
-    return null;        // should be impossible
+    return fileEntry;
   }
 
   // ---------------------------------------------------------------------------------//
-  public void addResourceFork (FileEntry fileEntry, byte[] dataBuffer, int eof)
+  public void addResourceFork (FileEntry fileEntry, byte[] fileBuffer, int eof)
       throws DiskFullException
   // ---------------------------------------------------------------------------------//
   {
     int blockNo = allocateNextBlock ();                 // allocate extended key block
 
     FileWriter fileWriter = new FileWriter (this);      // create resource fork
-    fileWriter.writeFile (dataBuffer, eof);
+    fileWriter.writeFile (fileBuffer, eof);
 
     ExtendedKeyBlock extendedKeyBlock = new ExtendedKeyBlock (this, blockNo * BLOCK_SIZE);
 
diff --git a/src/com/bytezone/diskbrowser/utilities/NuFX.java b/src/com/bytezone/diskbrowser/utilities/NuFX.java
index 00bafaf..a646339 100644
--- a/src/com/bytezone/diskbrowser/utilities/NuFX.java
+++ b/src/com/bytezone/diskbrowser/utilities/NuFX.java
@@ -8,6 +8,7 @@ import java.util.ArrayList;
 import java.util.List;
 
 import com.bytezone.diskbrowser.prodos.write.DiskFullException;
+import com.bytezone.diskbrowser.prodos.write.FileAlreadyExistsException;
 import com.bytezone.diskbrowser.prodos.write.FileEntry;
 import com.bytezone.diskbrowser.prodos.write.ProdosDisk;
 import com.bytezone.diskbrowser.prodos.write.VolumeCatalogFullException;
@@ -167,12 +168,14 @@ public class NuFX
             if (record.hasFile ())
             {
               String fileName = volumeName.convert (record.getFileName ());
+
               if (!record.isValidFileSystem ())
               {
                 System.out.printf ("File %s is file system %s%n", fileName,
                     record.getFileSystemName ());
                 continue;
               }
+
               //              int fileSize = record.getFileSize ();
               byte fileType = (byte) record.getFileType ();
               int eof = record.getUncompressedSize ();
@@ -185,9 +188,13 @@ public class NuFX
                 System.out.printf ("%3d %-35s %02X %,7d %,7d %,7d  %s  %s%n", ++count,
                     fileName, fileType, auxType, eof, buffer.length, created, modified);
 
-              FileEntry fileEntry =
-                  disk.addFile (fileName, fileType, auxType, created, modified, buffer);
-              if (fileEntry == null)
+              FileEntry fileEntry;
+              try
+              {
+                fileEntry = disk.addFile (fileName, fileType, auxType, created, modified,
+                    buffer, eof);
+              }
+              catch (FileAlreadyExistsException e)
               {
                 System.out.printf ("File %s not added%n", fileName);
                 break;
@@ -196,7 +203,6 @@ public class NuFX
               if (record.hasResource ())
               {
                 buffer = record.getResourceData ();
-                //                System.out.println (HexFormatter.format (buffer));
                 disk.addResourceFork (fileEntry, buffer, buffer.length);
               }
             }