diff --git a/lib_com/ivas_prot.h b/lib_com/ivas_prot.h
index 2eacf811b0d1d9556d79479d47f5ad84ec60d2d7..b27a002513cf656605b7148f1397b68b4b7c8bc3 100755
--- a/lib_com/ivas_prot.h
+++ b/lib_com/ivas_prot.h
@@ -5469,7 +5469,11 @@ void ivas_mono_dmx_renderer_close(
     MONO_DOWNMIX_RENDERER_HANDLE *hMonoDmxRenderer              /* i/ i/o: Mono downmix structure                       */
 );
 
+#ifdef NONBE_FIX_967_ISM_MONO_DMX
+void ivas_ism_mono_dmx(
+#else
 void ivas_mono_downmix_render_passive(
+#endif
     Decoder_Struct *st_ivas,                                    /* i/o: IVAS decoder structure                                */
     float *output_f[],                                          /* i/o: synthesized core-coder transport channels/mono output */
     const int16_t output_frame                                  /* i  : output frame length                                   */
diff --git a/lib_com/options.h b/lib_com/options.h
index 5aa3ec18d8999a901e5cf0e81920c308361dd033..94b49b848153684db4a3389cb33a4d759c49d02e 100755
--- a/lib_com/options.h
+++ b/lib_com/options.h
@@ -175,6 +175,7 @@
 #define NONBE_FIX_935_EARLY_REFLECTIONS_WRONG_ORDER           /* Qualcomm: issue 953: fix order or ER channels in LC mode*/
 #define NONBE_FIX_949_MC_5MS_FRAMING                          /* Dlb: issue 949: fix for issue 949, distorted output in MC mode with 5ms framing*/
 #define NONBE_FIX_952_MC_PARAMUPMIX_5MS                       /* Dlb : issue 952 : Differences between 5ms and 20ms rendering for ParamUpmix*/
+#define NONBE_FIX_967_ISM_MONO_DMX                            /* FhG: issue 967: accumulating energies in ISM mono DMX */
 #define NONBE_FIX_968_ISM_BRIR_WITH_HEADROTATION_5MS_FIX      /* FhG : issue #968: differences between 5ms and 20ms rendering for discrete ISM with BRIR and head rotation*/
 #define NONBE_FIX_977_OSBA_GAIN_MISMATCH                      /* Dlb : issue 977 : Output gain mismatch for different bit rates in OSBA */
 
diff --git a/lib_dec/ivas_jbm_dec.c b/lib_dec/ivas_jbm_dec.c
index b0199a301e7b65ba24afa794b63b9d065cdb4dcb..1b09291125dead66523bf95db9d9a8c4d6050734 100644
--- a/lib_dec/ivas_jbm_dec.c
+++ b/lib_dec/ivas_jbm_dec.c
@@ -196,7 +196,11 @@ ivas_error ivas_jbm_dec_tc(
 
         if ( st_ivas->renderer_type == RENDERER_MONO_DOWNMIX )
         {
+#ifdef NONBE_FIX_967_ISM_MONO_DMX
+            ivas_ism_mono_dmx( st_ivas, p_output, output_frame );
+#else
             ivas_mono_downmix_render_passive( st_ivas, p_output, output_frame );
+#endif
         }
         else if ( st_ivas->ism_mode == ISM_MODE_PARAM && ( st_ivas->renderer_type == RENDERER_BINAURAL_PARAMETRIC || st_ivas->renderer_type == RENDERER_BINAURAL_PARAMETRIC_ROOM || st_ivas->renderer_type == RENDERER_STEREO_PARAMETRIC ) )
         {
@@ -388,7 +392,11 @@ ivas_error ivas_jbm_dec_tc(
 
         if ( st_ivas->renderer_type == RENDERER_MONO_DOWNMIX )
         {
+#ifdef NONBE_FIX_967_ISM_MONO_DMX
+            ivas_ism_mono_dmx( st_ivas, p_output, output_frame );
+#else
             ivas_mono_downmix_render_passive( st_ivas, p_output, output_frame );
+#endif
         }
         else if ( output_config == IVAS_AUDIO_CONFIG_EXTERNAL )
         {
@@ -512,7 +520,11 @@ ivas_error ivas_jbm_dec_tc(
         }
         else if ( st_ivas->renderer_type == RENDERER_MONO_DOWNMIX && st_ivas->ism_mode == ISM_SBA_MODE_DISC )
         {
+#ifdef NONBE_FIX_967_ISM_MONO_DMX
+            ivas_ism_mono_dmx( st_ivas, p_output, output_frame );
+#else
             ivas_mono_downmix_render_passive( st_ivas, p_output, output_frame );
+#endif
 
             /* add W */
             for ( n = 0; n < nchan_out; n++ )
diff --git a/lib_dec/ivas_mono_dmx_renderer.c b/lib_dec/ivas_mono_dmx_renderer.c
index 0936209639d9388e7910919011740336be89bf28..1da119f0003496c9106c4e1d0668468e7a30b3c6 100644
--- a/lib_dec/ivas_mono_dmx_renderer.c
+++ b/lib_dec/ivas_mono_dmx_renderer.c
@@ -46,9 +46,11 @@
  * Local constants
  *------------------------------------------------------------------------*/
 
-#define DOWNMIX_ALPHA                         0.95f /* Smoothing coefficient */
-#define DOWNMIX_MAX_GAIN                      4.0f  /* Maximum allowed gain  */
-#define MONO_DOWNMIX_RENDERER_MAX_INPUT_CHANS 4
+#define DOWNMIX_ALPHA    0.95f /* Smoothing coefficient */
+#define DOWNMIX_MAX_GAIN 4.0f  /* Maximum allowed gain  */
+#ifndef NONBE_FIX_967_ISM_MONO_DMX
+#define MONO_DOWNMIX_RENDERER_MAX_INPUT_CHANS 4 // FhG esr: this seems to be obsolete; not related to issue 967
+#endif
 
 
 /*-------------------------------------------------------------------------
@@ -99,12 +101,16 @@ void ivas_mono_dmx_renderer_close(
 
 
 /*-------------------------------------------------------------------------
- * ivas_mono_downmix_render_passive()
+ * ivas_ism_mono_dmx()
  *
  * Downmix process
  *------------------------------------------------------------------------*/
 
+#ifdef NONBE_FIX_967_ISM_MONO_DMX
+void ivas_ism_mono_dmx(
+#else
 void ivas_mono_downmix_render_passive(
+#endif
     Decoder_Struct *st_ivas,   /* i/o: IVAS decoder structure                                */
     float *output_f[],         /* i/o: synthesized core-coder transport channels/mono output */
     const int16_t output_frame /* i  : output frame length                                   */
@@ -112,6 +118,9 @@ void ivas_mono_downmix_render_passive(
 {
     int16_t i, j, numInputChannels;
     float proto_signal[L_FRAME48k], eq;
+#ifdef NONBE_FIX_967_ISM_MONO_DMX
+    float inputEnergy_local, protoEnergy_local;
+#endif
     MONO_DOWNMIX_RENDERER_HANDLE hDownmix;
 
     numInputChannels = st_ivas->nSCE;
@@ -134,6 +143,10 @@ void ivas_mono_downmix_render_passive(
 
     hDownmix = st_ivas->hMonoDmxRenderer;
     set_zero( proto_signal, output_frame );
+#ifdef NONBE_FIX_967_ISM_MONO_DMX
+    inputEnergy_local = 0;
+    protoEnergy_local = 0;
+#endif
 
     /* Compute the Proto Signal */
     for ( i = 0; i < numInputChannels; i++ )
@@ -141,6 +154,18 @@ void ivas_mono_downmix_render_passive(
         v_add( output_f[i], proto_signal, proto_signal, output_frame );
     }
 
+#ifdef NONBE_FIX_967_ISM_MONO_DMX
+    /* compute the input energy, proto energy */
+    for ( i = 0; i < output_frame; i++ )
+    {
+        protoEnergy_local += proto_signal[i] * proto_signal[i];
+
+        for ( j = 0; j < numInputChannels; j++ )
+        {
+            inputEnergy_local += ( output_f[j][i] * output_f[j][i] );
+        }
+    }
+#else
     /* compute the input energy, proto energy after smoothing */
     hDownmix->inputEnergy *= DOWNMIX_ALPHA;
     hDownmix->protoEnergy *= DOWNMIX_ALPHA;
@@ -153,6 +178,13 @@ void ivas_mono_downmix_render_passive(
             hDownmix->inputEnergy += ( output_f[j][i] * output_f[j][i] );
         }
     }
+#endif
+#ifdef NONBE_FIX_967_ISM_MONO_DMX
+    hDownmix->inputEnergy *= DOWNMIX_ALPHA;
+    hDownmix->protoEnergy *= DOWNMIX_ALPHA;
+    hDownmix->inputEnergy += ( 1.0f - DOWNMIX_ALPHA ) * inputEnergy_local;
+    hDownmix->protoEnergy += ( 1.0f - DOWNMIX_ALPHA ) * protoEnergy_local;
+#endif
 
     /* compute the eq factor */
     eq = min( DOWNMIX_MAX_GAIN, sqrtf( hDownmix->inputEnergy / ( EPSILON + hDownmix->protoEnergy ) ) );
diff --git a/scripts/config/self_test.prm b/scripts/config/self_test.prm
index 203c8dfc4dfaac52fef159905799fa6c11f029fd..96cceba07c53958f3e28e9701af84a6ea7950c05 100644
--- a/scripts/config/self_test.prm
+++ b/scripts/config/self_test.prm
@@ -402,7 +402,7 @@ eid-xor -fer -vbr -bs g192 -ep g192 bit ../scripts/dly_error_profiles/ep_5pct.g1
 
 // 3 ISM with metadata at 48 kbps, 48 kHz in, 48 kHz out, EXT out
 ../IVAS_cod -ism 3 testv/stvISM1.csv testv/stvISM2.csv testv/stvISM3.csv 48000 48 testv/stv3ISM48s.wav bit
-../IVAS_dec MONO 48 bit testv/stv3ISM48s.48000_48-48_MONO.tst
+../IVAS_dec EXT 48 bit testv/stv3ISM48s.48000_48-48_MONO.tst
 
 // 3 ISM with metadata at 64 kbps, 48 kHz in, 48 kHz out, EXT out
 ../IVAS_cod -ism 3 testv/stvISM1.csv testv/stvISM2.csv testv/stvISM3.csv 64000 48 testv/stv3ISM48s.wav bit
diff --git a/scripts/config/self_test_ltv.prm b/scripts/config/self_test_ltv.prm
index 0aa3f764dc250b5bbe62c9ec69836189018a1f7c..971a577ed8db797e1615b9220d7091f330432447 100644
--- a/scripts/config/self_test_ltv.prm
+++ b/scripts/config/self_test_ltv.prm
@@ -401,7 +401,7 @@ eid-xor -fer -vbr -bs g192 -ep g192 bit ../scripts/dly_error_profiles/ep_5pct.g1
 
 // 3 ISM with metadata at 48 kbps, 48 kHz in, 48 kHz out, EXT out
 ../IVAS_cod -ism 3 testv/ltvISM1.csv testv/ltvISM2.csv testv/ltvISM3.csv 48000 48 testv/ltv48_3ISM.wav bit
-../IVAS_dec MONO 48 bit testv/ltv48_3ISM.48000_48-48_MONO.tst
+../IVAS_dec EXT 48 bit testv/ltv48_3ISM.48000_48-48_MONO.tst
 
 // 3 ISM with metadata at 64 kbps, 48 kHz in, 48 kHz out, EXT out
 ../IVAS_cod -ism 3 testv/ltvISM1.csv testv/ltvISM2.csv testv/ltvISM3.csv 64000 48 testv/ltv48_3ISM.wav bit