diff --git a/configure.ac b/configure.ac
index f4eb4c5a65f87a88edd18caff564341c27f5941c..dc7dfc29f6a753a64db5cc0d99069c5aa56a3508 100644
--- a/configure.ac
+++ b/configure.ac
@@ -124,6 +124,13 @@ AC_ARG_ENABLE(experimental-postfilter, [  --enable-experimental-postfilter     E
   AC_DEFINE([ENABLE_POSTFILTER], , [Postfilter])
 fi])
 
+ac_enable_custom_modes="no"
+AC_ARG_ENABLE(custom-modes, [  --enable-custom-modes        Enable non-Opus modes, like 44.1 kHz and powers of two ],
+[if test "$enableval" = yes; then
+  ac_enable_custom_modes="yes"
+  AC_DEFINE([CUSTOM_MODES], , [Custom modes])
+fi])
+
 float_approx=$has_float_approx
 AC_ARG_ENABLE(float-approx, [  --enable-float-approx   enable fast approximations for floating point],
     [ if test "$enableval" = yes; then
diff --git a/libcelt/modes.h b/libcelt/modes.h
index d874d7b8493e4ad8c40cb13990420b80445e9b6e..249ffacde2de06bce5ce512397fb8e287fdb83aa 100644
--- a/libcelt/modes.h
+++ b/libcelt/modes.h
@@ -41,7 +41,7 @@
 #include "entenc.h"
 #include "entdec.h"
 
-#define CELT_BITSTREAM_VERSION 0x8000000f
+#define CELT_BITSTREAM_VERSION 0x80000010
 
 #define MAX_PERIOD 1024