diff --git a/lib_com/ivas_prot.h b/lib_com/ivas_prot.h
index 9e15502344448017958a80e8d3b982b6ba9afae0..a191d1bf3967a79ca83e585388ea631f4cec20cd 100755
--- a/lib_com/ivas_prot.h
+++ b/lib_com/ivas_prot.h
@@ -5218,6 +5218,9 @@ void ivas_ism_renderer_close(
 
 void ivas_ism_render_sf(
     Decoder_Struct *st_ivas,                                    /* i/o: IVAS decoder structure                          */
+#ifdef NONBE_FIX_1021_ISM_BRIR_RS_FLUSH
+    const RENDERER_TYPE renderer_type,                          /* i  : active renderer type                            */
+#endif
     float *output_f[],                                          /* i/o: core-coder transport channels/object output     */
     const int16_t n_samples_to_render                           /* i  : output frame length per channel                 */
 );
diff --git a/lib_com/options.h b/lib_com/options.h
index a7d1d5fa5c9f6393953039e28f722556147f0ec9..7b6179c5c6652986470e948fdf476fa595bf98f9 100644
--- a/lib_com/options.h
+++ b/lib_com/options.h
@@ -167,6 +167,7 @@
 /* any switch which is non-be wrt selection floating point code */
 /* all switches in this category should start with "NONBE_" */
 
+#define NONBE_FIX_1021_ISM_BRIR_RS_FLUSH                      /* FhG: issue #1021: fix ISM with JBM and RS renderer flushing*/
 
 /* ##################### End NON-BE switches ########################### */
 
diff --git a/lib_dec/ivas_ism_renderer.c b/lib_dec/ivas_ism_renderer.c
index 7b321c523b80740d052f2ef276032d04cd8085b4..33e05a0e6a99c67be570a43642640a1e520fa0af 100644
--- a/lib_dec/ivas_ism_renderer.c
+++ b/lib_dec/ivas_ism_renderer.c
@@ -140,7 +140,10 @@ void ivas_ism_renderer_close(
  *-------------------------------------------------------------------------*/
 
 void ivas_ism_render_sf(
-    Decoder_Struct *st_ivas,          /* i/o: IVAS decoder structure                      */
+    Decoder_Struct *st_ivas, /* i/o: IVAS decoder structure                      */
+#ifdef NONBE_FIX_1021_ISM_BRIR_RS_FLUSH
+    const RENDERER_TYPE renderer_type, /* i  : active renderer type                        */
+#endif
     float *output_f[],                /* i/o: core-coder transport channels/object output */
     const int16_t n_samples_to_render /* i  : output frame length per channel             */
 )
@@ -172,12 +175,15 @@ void ivas_ism_render_sf(
     assert( slots_to_render == 0 );
     assert( last_sf <= st_ivas->hTcBuffer->nb_subframes );
 #endif
-
+#ifdef NONBE_FIX_1021_ISM_BRIR_RS_FLUSH
+    num_objects = st_ivas->nchan_ism;
+#else
     num_objects = st_ivas->nchan_transport;
     if ( st_ivas->ivas_format == SBA_ISM_FORMAT )
     {
         num_objects = st_ivas->nchan_ism;
     }
+#endif
 
     nchan_out_woLFE = st_ivas->hIntSetup.nchan_out_woLFE;
 
@@ -282,7 +288,11 @@ void ivas_ism_render_sf(
         n_samples_rendered_loop += n_samples_in_subframe;
         /* update rendered subframe and slots info for all cases apart from a following crend call, the update will
            then happen in the crend call*/
+#ifdef NONBE_FIX_1021_ISM_BRIR_RS_FLUSH
+        if ( renderer_type != RENDERER_BINAURAL_MIXER_CONV_ROOM )
+#else
         if ( st_ivas->renderer_type != RENDERER_BINAURAL_MIXER_CONV_ROOM )
+#endif
         {
             st_ivas->hTcBuffer->subframes_rendered += 1;
             st_ivas->hTcBuffer->slots_rendered += st_ivas->hTcBuffer->subframe_nbslots[subframe_idx];
diff --git a/lib_dec/ivas_jbm_dec.c b/lib_dec/ivas_jbm_dec.c
index c7ad64a60afbba35711ec1cc73babb9a64489e9f..1c550fa68f77e49e5bbbdaad70db6bcdfdbe2d80 100644
--- a/lib_dec/ivas_jbm_dec.c
+++ b/lib_dec/ivas_jbm_dec.c
@@ -1093,7 +1093,11 @@ ivas_error ivas_jbm_dec_render(
             if ( st_ivas->renderer_type == RENDERER_TD_PANNING || st_ivas->renderer_type == RENDERER_BINAURAL_MIXER_CONV_ROOM )
             {
                 /* Convert to CICPxx; used also for ISM->CICP19->binaural_room rendering */
+#ifdef NONBE_FIX_1021_ISM_BRIR_RS_FLUSH
+                ivas_ism_render_sf( st_ivas, st_ivas->renderer_type, p_output, *nSamplesRendered );
+#else
                 ivas_ism_render_sf( st_ivas, p_output, *nSamplesRendered );
+#endif
             }
             else if ( st_ivas->renderer_type == RENDERER_NON_DIEGETIC_DOWNMIX )
             {
@@ -1231,7 +1235,11 @@ ivas_error ivas_jbm_dec_render(
                 }
 
                 /* render objects */
+#ifdef NONBE_FIX_1021_ISM_BRIR_RS_FLUSH
+                ivas_ism_render_sf( st_ivas, st_ivas->renderer_type, p_output, *nSamplesRendered );
+#else
                 ivas_ism_render_sf( st_ivas, p_output, *nSamplesRendered );
+#endif
 
                 /* add already rendered SBA part */
                 for ( n = 0; n < nchan_out; n++ )
@@ -1628,7 +1636,11 @@ ivas_error ivas_jbm_dec_flush_renderer(
                     /* Convert to CICPxx; used also for ISM->CICP19->binaural_room rendering */
                     set_f( st_ivas->hIsmRendererData->interpolator, 1.0f, hTcBuffer->n_samples_granularity );
 
+#ifdef NONBE_FIX_1021_ISM_BRIR_RS_FLUSH
+                    ivas_ism_render_sf( st_ivas, renderer_type_old, p_output, hTcBuffer->n_samples_granularity );
+#else
                     ivas_ism_render_sf( st_ivas, p_output, hTcBuffer->n_samples_granularity );
+#endif
 
 #if defined SPLIT_REND_WITH_HEAD_ROT
                     if ( ( error = ivas_rend_crendProcessSubframe( st_ivas->hCrendWrapper, IVAS_AUDIO_CONFIG_7_1_4, IVAS_AUDIO_CONFIG_BINAURAL_ROOM_IR, st_ivas->hDecoderConfig, NULL,
diff --git a/lib_dec/ivas_osba_dec.c b/lib_dec/ivas_osba_dec.c
index 6585db587e12be2c683a5c4edafeb23bdd76f3d0..65e05f78be7ca22ed2063d4196bba570bddb9241 100644
--- a/lib_dec/ivas_osba_dec.c
+++ b/lib_dec/ivas_osba_dec.c
@@ -284,7 +284,11 @@ ivas_error ivas_osba_render_sf(
 
     if ( st_ivas->renderer_type != RENDERER_BINAURAL_FASTCONV_ROOM )
     {
+#ifdef NONBE_FIX_1021_ISM_BRIR_RS_FLUSH
+        ivas_ism_render_sf( st_ivas, st_ivas->renderer_type, p_output_ism, *nSamplesRendered );
+#else
         ivas_ism_render_sf( st_ivas, p_output_ism, *nSamplesRendered );
+#endif
     }
 
     for ( n = 0; n < st_ivas->hDecoderConfig->nchan_out; n++ )