diff --git a/gio/Gio.metadata b/gio/Gio.metadata
index b80aa5712..59a390dc1 100644
--- a/gio/Gio.metadata
+++ b/gio/Gio.metadata
@@ -30,6 +30,8 @@
   <attr path="/api/namespace/interface[@cname='GIcon']" name="consume_only">1</attr>
   <attr path="/api/namespace/interface[@cname='GMount']" name="consume_only">1</attr>
   <attr path="/api/namespace/interface[@cname='GMount']/method[@name='CanUnmount']" name="name">GetCanUnmount</attr>
+  <attr path="/api/namespace/interface[@cname='GMount']/method[@name='GuessContentTypeFinish']/return-type" name="null_term_array">1</attr>
+  <attr path="/api/namespace/interface[@cname='GMount']/method[@name='GuessContentTypeSync']/return-type" name="null_term_array">1</attr>
   <attr path="/api/namespace/interface[@cname='GSeekable']/method[@cname='g_seekable_can_seek']" name="name">GetCanSeek</attr>
   <attr path="/api/namespace/interface[@cname='GSeekable']/method[@cname='g_seekable_tell']" name="name">GetPosition</attr>
   <attr path="/api/namespace/interface[@cname='GTlsServerConnection']/property[@cname='authentication-mode']" name="hidden">1</attr>
diff --git a/gio/GioStream.cs b/gio/GioStream.cs
index 03d1696f1..631549244 100644
--- a/gio/GioStream.cs
+++ b/gio/GioStream.cs
@@ -63,6 +63,14 @@ namespace GLib
 			can_seek = stream is Seekable && (stream as Seekable).CanSeek;
 		}
 
+		public GioStream (IOStream stream)
+		{
+			this.stream = stream;
+			can_read = true;
+			can_write = true;
+			can_seek = stream is Seekable && (stream as Seekable).CanSeek;
+		}
+
 		public override bool CanSeek {
 			get { return can_seek; }
 		}
@@ -90,6 +98,10 @@ namespace GLib
 					FileInfo info = (stream as FileOutputStream).QueryInfo ("standard::size", null);
 					return info.Size;
 				}
+				if (stream is FileIOStream) {
+					FileInfo info = (stream as FileIOStream).QueryInfo ("standard::size", null);
+					return info.Size;
+				}
 				throw new NotImplementedException (String.Format ("not implemented for {0} streams", stream.GetType()));
 			}
 		}
@@ -127,7 +139,11 @@ namespace GLib
 				throw new NotSupportedException ("The stream does not support reading");
 			if (is_disposed)
 				throw new ObjectDisposedException ("The stream is closed");
-			InputStream input_stream = stream as InputStream;
+			InputStream input_stream = null;
+			if (stream is InputStream)
+				input_stream = stream as InputStream;
+			else if (stream is IOStream)
+				input_stream = (stream as IOStream).InputStream;
 			if (input_stream == null)
 				throw new System.Exception ("this shouldn't happen");
 
@@ -155,7 +171,11 @@ namespace GLib
 				throw new NotSupportedException ("The stream does not support writing");
 			if (is_disposed)
 				throw new ObjectDisposedException ("The stream is closed");
-			OutputStream output_stream = stream as OutputStream;
+			OutputStream output_stream = null;
+			if (stream is OutputStream)
+				output_stream = stream as OutputStream;
+			else if (stream is IOStream)
+				output_stream = (stream as IOStream).OutputStream;
 			if (output_stream == null)
 				throw new System.Exception ("this shouldn't happen");
 			if (offset == 0) {
@@ -198,9 +218,16 @@ namespace GLib
 		{
 			if (!CanSeek || !CanWrite)
 				throw new NotSupportedException ("This stream doesn't support seeking");
+
+			var seekable = stream as Seekable;
+
+			if (!seekable.CanTruncate ())
+				throw new NotSupportedException ("This stream doesn't support truncating");
+
 			if (is_disposed)
 				throw new ObjectDisposedException ("The stream is closed");
-			throw new NotImplementedException ();
+
+			seekable.Truncate (value, null);
 		}
 
 		public override void Close ()
@@ -209,6 +236,8 @@ namespace GLib
 				(stream as InputStream).Close (null);
 			if (stream is OutputStream)
 				(stream as OutputStream).Close (null);
+			if (stream is IOStream)
+				(stream as IOStream).Close (null);
 			is_disposed = true;
 		}
 	}