diff --git a/src/org/jruby/RubyFile.java b/src/org/jruby/RubyFile.java
index 4453aa0ca05..80d4dc25689 100644
--- a/src/org/jruby/RubyFile.java
+++ b/src/org/jruby/RubyFile.java
@@ -331,7 +331,19 @@ public IRubyObject initialize19(ThreadContext context, IRubyObject[] args, Block
             }
         }
 
-        return openFile19(context, args);
+        RubyBoolean hasOffset = context.runtime.newBoolean(false);
+        if (args[args.length - 1] instanceof RubyBoolean) {
+            hasOffset = (RubyBoolean) args[args.length - 1];
+            IRubyObject[] newArgs = new IRubyObject[args.length - 1];
+            System.arraycopy(args, 0, newArgs, 0, newArgs.length);
+            args = newArgs;
+        }
+
+        if(hasOffset.isTrue()) {
+            return openFile19(context, args, true);
+        } else {
+            return openFile19(context, args, false);
+        }
     }
 
     @JRubyMethod(required = 1)
@@ -1104,8 +1116,11 @@ public void setEncoding(Encoding encoding) {
         // :)
     }
 
-    // mri: rb_open_file + rb_scan_open_args
     private IRubyObject openFile19(ThreadContext context, IRubyObject args[]) {
+        return openFile19(context, args, false);
+    }
+    // mri: rb_open_file + rb_scan_open_args
+    private IRubyObject openFile19(ThreadContext context, IRubyObject args[], boolean hasOffeset) {
         Ruby runtime = context.runtime;
         RubyString filename = get_path(context, args[0]);
 
@@ -1147,7 +1162,7 @@ private IRubyObject openFile19(ThreadContext context, IRubyObject args[]) {
         int perm = (pm[EncodingUtils.PERM] != null && !pm[EncodingUtils.PERM].isNil()) ? 
                 RubyNumeric.num2int(pm[EncodingUtils.PERM]) : 0666;
         
-        sysopenInternal(path, ModeFlags.createModeFlags(oflags), perm);
+        sysopenInternal(path, ModeFlags.createModeFlags(oflags), perm, hasOffeset);
 
         return this;
     }
@@ -1184,8 +1199,12 @@ private int getFilePermissions(IRubyObject[] args) {
         return (args.length > 2 && !args[2].isNil()) ? RubyNumeric.num2int(args[2]) : 438;
     }
 
-    // mri: rb_file_open_generic
     protected void sysopenInternal(String path, ModeFlags modes, int perm) {
+        sysopenInternal(path, modes, perm, false);
+    }
+
+    // mri: rb_file_open_generic
+    protected void sysopenInternal(String path, ModeFlags modes, int perm, boolean hasOffset) {
         if (path.startsWith("jar:")) path = path.substring(4);
         
         openFile = new OpenFile();
@@ -1196,7 +1215,7 @@ protected void sysopenInternal(String path, ModeFlags modes, int perm) {
         int umask = getUmaskSafe( getRuntime() );
         perm = perm - (perm & umask);
 
-        ChannelDescriptor descriptor = sysopen(path, modes, perm);
+        ChannelDescriptor descriptor = sysopen(path, modes, perm, hasOffset);
         openFile.setMainStream(fdopen(descriptor, modes));
         if (hasBom) {
             // FIXME: Wonky that we acquire RubyEncoding to pass these encodings through
@@ -1238,6 +1257,10 @@ protected void openInternal(String path, String modeString) {
     }
 
     private ChannelDescriptor sysopen(String path, ModeFlags modes, int perm) {
+        return sysopen(path,modes,perm,false);
+    }
+
+    private ChannelDescriptor sysopen(String path, ModeFlags modes, int perm, boolean hasOffset) {
         try {
             ChannelDescriptor descriptor = ChannelDescriptor.open(
                     getRuntime().getCurrentDirectory(),
@@ -1245,7 +1268,8 @@ private ChannelDescriptor sysopen(String path, ModeFlags modes, int perm) {
                     modes,
                     perm,
                     getRuntime().getPosix(),
-                    getRuntime().getJRubyClassLoader());
+                    getRuntime().getJRubyClassLoader(),
+                    hasOffset);
 
             // TODO: check if too many open files, GC and try again
 
diff --git a/src/org/jruby/RubyIO.java b/src/org/jruby/RubyIO.java
index dab48ee571b..71a0fbd19ab 100644
--- a/src/org/jruby/RubyIO.java
+++ b/src/org/jruby/RubyIO.java
@@ -3605,11 +3605,17 @@ private static IRubyObject read19(ThreadContext context, IRubyObject recv, IRuby
      */
     private static IRubyObject write19(ThreadContext context, IRubyObject recv, IRubyObject path, IRubyObject str, IRubyObject offset, RubyHash options) {
         // FIXME: process options
+        Ruby runtime = context.runtime;
+
+        IRubyObject hasOffset = runtime.getNil();
+
+        if (!offset.isNil()) hasOffset = runtime.newBoolean(true);
+        else hasOffset = runtime.newBoolean(false);
 
         RubyString pathStr = RubyFile.get_path(context, path);
-        Ruby runtime = context.runtime;
+
         failIfDirectory(runtime, pathStr);
-        RubyIO file = newFile(context, recv, pathStr, context.runtime.newString("w"));
+        RubyIO file = newFile(context, recv, pathStr, context.runtime.newString("w"), hasOffset);
 
         try {
             if (!offset.isNil()) file.seek(context, offset);
diff --git a/src/org/jruby/util/io/ChannelDescriptor.java b/src/org/jruby/util/io/ChannelDescriptor.java
index e8762cf78bd..2c92f1bf2fc 100644
--- a/src/org/jruby/util/io/ChannelDescriptor.java
+++ b/src/org/jruby/util/io/ChannelDescriptor.java
@@ -790,6 +790,10 @@ public static ChannelDescriptor open(String cwd, String path, ModeFlags flags, i
      * @throws java.io.IOException if there is an exception during IO
      */
     public static ChannelDescriptor open(String cwd, String path, ModeFlags flags, int perm, POSIX posix, ClassLoader classLoader) throws FileNotFoundException, DirectoryAsFileException, FileExistsException, IOException {
+        return open(cwd, path, flags, perm, posix, classLoader, false);
+    }
+
+    public static ChannelDescriptor open(String cwd, String path, ModeFlags flags, int perm, POSIX posix, ClassLoader classLoader, boolean hasOffset) throws FileNotFoundException, DirectoryAsFileException, FileExistsException, IOException {
         boolean fileCreated = false;
         if (path.equals("/dev/null") || path.equalsIgnoreCase("nul:") || path.equalsIgnoreCase("nul")) {
             Channel nullChannel = new NullChannel();
@@ -865,7 +869,7 @@ public static ChannelDescriptor open(String cwd, String path, ModeFlags flags, i
             FileChannel fileChannel;
             boolean isInAppendMode;
             if (flags.isWritable() && !flags.isReadable()) {
-                FileOutputStream fos = new FileOutputStream(theFile, flags.isAppendable());
+                RandomAccessFile fos = new RandomAccessFile(theFile, flags.toJavaModeString());
                 fileChannel = fos.getChannel();
                 fileDescriptor = fos.getFD();
                 isInAppendMode = true;
@@ -887,7 +891,7 @@ public static ChannelDescriptor open(String cwd, String path, ModeFlags flags, i
             }
 
             try {
-                if (flags.isTruncate()) fileChannel.truncate(0);
+                if (flags.isTruncate() && !hasOffset) fileChannel.truncate(0);
             } catch (IOException ioe) {
                 if (ioe.getMessage().equals("Illegal seek")) {
                     // ignore; it's a pipe or fifo that can't be truncated