diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index e14cfd90..2e42ce4a 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -11,6 +11,7 @@ UNRELEASED
   * FIXED:     Incorrect internal input EP count for input only devices
   * ADDED:     MIDI unit and subsystem tests
   * FIXED:     ADAT Tx called too frequently
+  * FIXED:     Initialise SMUX based on DEFAULT_FREQ in clockgen
 
 4.0.0
 -----
diff --git a/lib_xua/src/core/clocking/clockgen.xc b/lib_xua/src/core/clocking/clockgen.xc
index c75f56e4..ac172b8f 100644
--- a/lib_xua/src/core/clocking/clockgen.xc
+++ b/lib_xua/src/core/clocking/clockgen.xc
@@ -235,7 +235,23 @@ void clockGen ( streaming chanend ?c_spdif_rx,
     unsigned tmp;
 
     /* Start in no-SMUX (8-channel) mode */
-    int smux = 0;
+    int smux;
+    // Initialise smux based based on the DEFAULT_FREQ
+    if(DEFAULT_FREQ < 88200)
+    {
+        /* No SMUX */
+        smux = 0;
+    }
+    else if(DEFAULT_FREQ < 176400)
+    {
+        /* SMUX */
+        smux = 1;
+    }
+    else
+    {
+        /* SMUX II */
+        smux = 2;
+    }
 
 #ifdef LEVEL_METER_LEDS
     timer t_level;