Index: src/org/jruby/util/IOHandlerSeekable.java
===================================================================
--- src/org/jruby/util/IOHandlerSeekable.java	(revision 2170)
+++ src/org/jruby/util/IOHandlerSeekable.java	(working copy)
@@ -250,7 +250,11 @@
             return 0;
         }
         
-        file.writeBytes(buf);
+        if (getModes().isBinary()) {
+            file.writeBytes(buf);
+        } else {
+            file.write(buf.getBytes());
+        }
             
         if (isSync()) {
             sync();