diff --git a/lib_com/options.h b/lib_com/options.h
index 3b1434ddd9480f7f801fbb1d4f74d302365c4b1f..7d55c32792597473ab667e8581f611d27fe724f9 100644
--- a/lib_com/options.h
+++ b/lib_com/options.h
@@ -172,6 +172,7 @@
 #define BE_FIX_832_ASAN_ERROR_EFAP_OSBA                       /* FhG: issue #832: fix ASAN error caused by re-allocating EFAP memories in OSBA*/
 #define NONBE_FIX_819_DOUBLE_PREC_COMB_FORMATS                /* VA: issue 820: Double precision arithmetic in combined formats */
 #define NONBE_FIX_849_OMASA_BFI_CRASH                         /* VA: issue 849: fix OMASA 2TC and FEC crashes */
+#define NONBE_FIX_856_TCX_LTP_SYNTH_FILTER                    /* FhG: issue 856: correct filtering length for tcx-ltp synth filtering*/
 
 #define NONBE_UNIFIED_DECODING_PATHS                          /* FhG: unify decoding paths   */
 #define NONBE_FIX_861_MASA_CRASH_STEREO_SWITCHING             /* VA: issue 861: fix MASA 2TC crash when switching from MDCT stereo to TD/DFT stereo */
diff --git a/lib_com/tcx_ltp.c b/lib_com/tcx_ltp.c
old mode 100644
new mode 100755
index 90dcb1515ce6bd332f2311975c12b9741ec828a2..502328348df6501804da45227e4e2949f9259f6a
--- a/lib_com/tcx_ltp.c
+++ b/lib_com/tcx_ltp.c
@@ -740,7 +740,11 @@ static void tcx_ltp_synth_filter_11_unequal_pitch(
     gain = prev_gain;
     gain_step = -prev_gain / length;
 
+#ifdef NONBE_FIX_856_TCX_LTP_SYNTH_FILTER
+    for ( j = 0; j < length; j++ )
+#else
     for ( j = 0; j < length + L; j++ )
+#endif
     {
         s = 0;
         s2 = 0;
@@ -761,8 +765,14 @@ static void tcx_ltp_synth_filter_11_unequal_pitch(
         gain += gain_step;
     }
 
+#ifdef NONBE_FIX_856_TCX_LTP_SYNTH_FILTER
+    mvr2r( out - L, temp_buf, length + L );
+    mvr2r( in + length, temp_buf + length + L, L );
+    temp_ptr = &temp_buf[0] + L;
+#else
     mvr2r( out - MAX_TCX_LTP_FILTER_LEN, temp_buf, MAX_TRANSITION_LEN + 2 * MAX_TCX_LTP_FILTER_LEN );
     temp_ptr = &temp_buf[0] + MAX_TCX_LTP_FILTER_LEN;
+#endif
 
     m0 = temp_ptr;
     m1 = temp_ptr - 1;