diff --git a/src/modules/audio_coding/main/source/audio_coding_module_impl.cc b/src/modules/audio_coding/main/source/audio_coding_module_impl.cc
index 7878210e9d..1d4514b4b9 100644
--- a/src/modules/audio_coding/main/source/audio_coding_module_impl.cc
+++ b/src/modules/audio_coding/main/source/audio_coding_module_impl.cc
@@ -902,10 +902,16 @@ with the previously registered codec");
             _isFirstRED = true;
         }
 
+        // If packet size or number of channels has changed, we need to
+        // re-initialize the encoder.
         if(_sendCodecInst.pacsize != sendCodec.pacsize)
         {
             forceInit = true;
         }
+        if(_sendCodecInst.channels != sendCodec.channels)
+        {
+            forceInit = true;
+        }
 
         if(forceInit)
         {
@@ -927,6 +933,7 @@ with the previously registered codec");
 
             _sendCodecInst.plfreq = sendCodec.plfreq;
             _sendCodecInst.pacsize = sendCodec.pacsize;
+            _sendCodecInst.channels = sendCodec.channels;
         }
 
         // If the change of sampling frequency has been successful then
diff --git a/src/modules/audio_coding/main/test/TestStereo.cpp b/src/modules/audio_coding/main/test/TestStereo.cpp
index a8618f08ad..c39d412148 100644
--- a/src/modules/audio_coding/main/test/TestStereo.cpp
+++ b/src/modules/audio_coding/main/test/TestStereo.cpp
@@ -456,10 +456,14 @@ WebRtc_Word16 TestStereo::RegisterSendCodec(char side,
     CHECK_ERROR(AudioCodingModule::Codec(codecName, myCodecParam, samplingFreqHz));
     myCodecParam.rate = rate;
     myCodecParam.pacsize = packSize;
+    // Start with register codec as mono, to test that changing to stereo works.
+    myCodecParam.channels = 1;
+    CHECK_ERROR(myACM->RegisterSendCodec(myCodecParam));
+    // Register codec as stereo.
     myCodecParam.channels = 2;
     CHECK_ERROR(myACM->RegisterSendCodec(myCodecParam));
 
-    // initialization was succesful
+    // Initialization was successful.
     return 0;
 }