diff --git a/src/lpcnet_quant.c b/src/lpcnet_quant.c
index 1b6f67f..11b40f2 100644
--- a/src/lpcnet_quant.c
+++ b/src/lpcnet_quant.c
@@ -136,7 +136,8 @@ void quant_pred_mbest(float vec_out[],
                       int num_stages,
                       float vq[],
                       int m[], int k,
-                      int mbest_survivors)
+                      int mbest_survivors,
+                      float ber)
 {
     float err[k], w[k], se1;
     int i,j,s,s1,ind;
@@ -205,15 +206,16 @@ void quant_pred_mbest(float vec_out[],
     if (lpcnet_fsv != NULL) fprintf(lpcnet_fsv, "%f\t%f\t", vec_in[0],sqrt(se1));
     if (lpcnet_verbose) fprintf(stderr, "    se1: %f\n", se1);
 
-//#define INSERT_ERROR
-#ifdef INSERT_ERROR
-    /* insert random errors in bits of first stage to test index optimisation */
-    for (s=0; s<num_stages; s++) {
-        for(int b=0; b<12; b++)
-            if ((float)rand()/RAND_MAX < 0.01)
-                indexes[s] ^= 1<<b;
+    if (ber > 0.0) {
+        /* optionally insert random errors in indexes to test index optimisation */
+        for (s=0; s<num_stages; s++) {
+            int log2m = roundf(log2(m[s]));
+            for(int b=0; b<log2m; b++)
+                if ((float)rand()/RAND_MAX < ber)
+                    indexes[s] ^= 1<<b;
+        }
     }
-#endif    
+    
     quant_pred_output(vec_out, indexes, err, pred, num_stages, vq, k);
     
     for(i=0; i<num_stages; i++)
@@ -385,7 +387,7 @@ int lpcnet_features_to_frame(LPCNET_QUANT *q, float features[], char frame[]) {
                 
     /* non-interpolated frame ----------------------------------------*/
 
-    quant_pred_mbest(q->features_quant, indexes, features, q->pred, q->num_stages, q->vq, q->m, k, q->mbest);
+    quant_pred_mbest(q->features_quant, indexes, features, q->pred, q->num_stages, q->vq, q->m, k, q->mbest, 0.0);
     pitch_ind = pitch_encode(features[2*NB_BANDS], q->pitch_bits);
     pitch_gain_ind =  pitch_gain_encode(features[2*NB_BANDS+1]);
     pack_frame(q->num_stages, q->m, indexes, q->pitch_bits, pitch_ind, pitch_gain_ind, frame);
diff --git a/src/lpcnet_quant.h b/src/lpcnet_quant.h
index f55b8bc..6a43519 100644
--- a/src/lpcnet_quant.h
+++ b/src/lpcnet_quant.h
@@ -67,7 +67,8 @@ void quant_pred_mbest(float vec_out[],  /* prev quant vector, and output, need t
                       int num_stages,
                       float vq[],
                       int m[], int k,
-                      int mbest_survivors);
+                      int mbest_survivors,
+                      float ber);
 
 void quant_pred_output(float vec_out[],
                        int   indexes[],
diff --git a/src/quant_feat.c b/src/quant_feat.c
index 7c8c1c0..6b3530d 100644
--- a/src/quant_feat.c
+++ b/src/quant_feat.c
@@ -64,11 +64,13 @@ int main(int argc, char *argv[]) {
     int   pitch_bits = 0;
     int   small_vec = 0;
     int   logmag = 0;
+    float ber = 0.0;
     
     for(i=0; i<MAX_STAGES*NB_BANDS*MAX_ENTRIES; i++) vq[i] = 0.0;
     
     static struct option long_options[] = {
         {"small",      required_argument, 0, 'a'},
+        {"ber",        required_argument, 0, 'b'},
         {"decimate",   required_argument, 0, 'd'},
         {"extpitch",   required_argument, 0, 'e'},
         {"first",      required_argument, 0, 'f'},
@@ -90,13 +92,17 @@ int main(int argc, char *argv[]) {
 
     int opt_index = 0;
     
-    while ((c = getopt_long (argc, argv, "ad:q:vs:f:p:e:u:l:m:h:wg:o:ix:", long_options, &opt_index)) != -1) {
+    while ((c = getopt_long (argc, argv, "ab:d:q:vs:f:p:e:u:l:m:h:wg:o:ix:", long_options, &opt_index)) != -1) {
         switch (c) {
         case 'a':
             /* small vec - zero out higher order bands */
             small_vec = 1;
             break;
-       case 'f':
+        case 'b':
+            ber = atof(optarg);
+            fprintf(stderr, "BER = %f\n", ber);
+            break;
+        case 'f':
             /* start VQ at band first+1 */
             first = atoi(optarg);
             k = NB_BANDS-first;
@@ -195,6 +201,7 @@ int main(int argc, char *argv[]) {
             break;
          default:
             fprintf(stderr,"usage: %s [Options]:\n  [-d --decimation 1/2/3...]\n  [-q --quant quantfile1,quantfile2,....]\n", argv[0]);
+            fprintf(stderr,"  [-b --ber BER Insert random bit errors in mag VQ indexes (default 0.0)]\n");
             fprintf(stderr,"  [-g --gain pitch gain bias]\n");
             fprintf(stderr,"  [-h --hard lowerLimitdB\n");
             fprintf(stderr,"  [-i --mag\n");
@@ -329,7 +336,8 @@ int main(int argc, char *argv[]) {
                 if (num_stages) {
                     if (mbest_survivors) {
                         /* mbest predictive VQ */
-                        quant_pred_mbest(&features_quant[first], indexes, &features[first], pred, num_stages, vq, m, k, mbest_survivors);
+                        quant_pred_mbest(&features_quant[first], indexes, &features[first], pred, num_stages,
+                                         vq, m, k, mbest_survivors, ber);
                     }
                     else {
                         /* standard predictive VQ */
diff --git a/src/quant_test.c b/src/quant_test.c
index ec0a9c2..40fd515 100644
--- a/src/quant_test.c
+++ b/src/quant_test.c
@@ -202,7 +202,7 @@ int main(int argc, char *argv[]) {
         if ((f % dec) == 0) {
             /* non-interpolated frame ----------------------------------------*/
 
-            quant_pred_mbest(features_quant_, indexes, features, pred, num_stages, vq, m, k, mbest_survivors);
+            quant_pred_mbest(features_quant_, indexes, features, pred, num_stages, vq, m, k, mbest_survivors, 0.0);
             pitch_ind = pitch_encode(features[2*NB_BANDS], pitch_bits);
             pitch_gain_ind =  pitch_gain_encode(features[2*NB_BANDS+1]);
             pack_frame(num_stages, m, indexes, pitch_bits, pitch_ind, pitch_gain_ind, frame);