diff --git a/gio/GioStream.cs b/gio/GioStream.cs
index 259d9d5f3..631549244 100644
--- a/gio/GioStream.cs
+++ b/gio/GioStream.cs
@@ -218,9 +218,16 @@ public override void SetLength (long value)
 		{
 			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 ()