diff --git a/src/codec/context.rs b/src/codec/context.rs
index d17b47a..f2df4d0 100644
--- a/src/codec/context.rs
+++ b/src/codec/context.rs
@@ -1,4 +1,4 @@
-use std::ops::Deref;
+use std::ops::{Deref, DerefMut};
 use std::ptr;
 
 use libc::c_int;
@@ -204,3 +204,9 @@ impl Deref for Opened {
 		&self.0
 	}
 }
+
+impl DerefMut for Opened {
+	fn deref_mut(&mut self) -> &mut<Self as Deref>::Target {
+		&mut self.0
+	}
+}