diff --git a/lib_com/options.h b/lib_com/options.h
index 3949dd4672616c6d0b27bf2d55067bfcad8cf124..fbfe61d36dd31f9b2d934c175675fd011eb6e1fc 100644
--- a/lib_com/options.h
+++ b/lib_com/options.h
@@ -82,6 +82,8 @@
 #define FIX_ISSUE_1817_REPLACE_CARRY_OVERFLOW                /* FhG: bit-exact, replace carry and overflow operations by 64-bit operations, MR 1931 */
 #define	NONBE_SVD_OPTIMIZATION                               /* FhG: reduce WMOPS of HouseHolderReduction() in ivas_svd_dec.c() by removing redundant mathematics and using 64 bit additions */
 #define FIX_1766_TCX2ACELP_BWE_ISSUE                         /* VA : Fix rare BWE issue when switching from TCX to ACELP */
+#define FIX_1781_SPECTRAL_GAPS                               /* FhG: Change internal calculation of tcx_noise_factor_ivas_fx() to 32-bit*/
+
 
 /* #################### Start BASOP porting switches ############################ */
 
diff --git a/lib_enc/tcx_utils_enc_fx.c b/lib_enc/tcx_utils_enc_fx.c
index 0face2cf4eb254777bff6d0c03dd7a820e00bbb3..a6e0a3e8010af8eb43edf77efa003edd86bf9ec8 100644
--- a/lib_enc/tcx_utils_enc_fx.c
+++ b/lib_enc/tcx_utils_enc_fx.c
@@ -2509,7 +2509,12 @@ void tcx_noise_factor_ivas_fx(
     Word16 i, k, win, segmentOffset, j;
     Word32 sqErrorNrg = 0, n;
     move32();
+#ifdef FIX_1781_SPECTRAL_GAPS
+    Word32 inv_gain2, tilt_factor;
+    Word16 inv_gain2_e, nTransWidth_1, exp_sqErrorNrg = 0;
+#else
     Word16 inv_gain2, inv_gain2_e, tilt_factor, nTransWidth_1, exp_sqErrorNrg = 0;
+#endif
     move16();
     Word32 accu1, accu2, tmp32;
     Word16 tmp1, tmp2, s;
@@ -2539,13 +2544,25 @@ void tcx_noise_factor_ivas_fx(
     /* tilt_factor = 1.0f /(float)pow(max(0.375f, tiltCompFactor), 1.0f/(float)L_frame); */
     tmp32 = BASOP_Util_Log2( L_deposit_h( s_max( 0x3000, tiltCompFactor ) ) ); /* 6Q25 */
     tmp32 = L_shr( Mpy_32_16_1( tmp32, negate( tmp1 ) ), 6 );
+#ifdef FIX_1781_SPECTRAL_GAPS
+    tilt_factor = BASOP_Util_InvLog2( L_sub( tmp32, 0x2000000 ) ); /* 1Q30 */
+#else
     tilt_factor = round_fx( BASOP_Util_InvLog2( L_sub( tmp32, 0x2000000 ) ) ); /* 1Q14 */
+#endif
 
     /* inv_gain2 = 1.0f / ((float)(nTransWidth * nTransWidth) * gain_tcx); */
     tmp32 = L_mult( imult1616( nTransWidth, nTransWidth ), gain_tcx ); /* 15Q16 */
+#ifdef FIX_1781_SPECTRAL_GAPS
+    inv_gain2 = BASOP_Util_Divide3232_Scale_newton( MAX_32, tmp32, &inv_gain2_e );
+#else
     inv_gain2 = BASOP_Util_Divide3232_Scale( MAX_32, tmp32, &inv_gain2_e );
+#endif
     inv_gain2_e = add( inv_gain2_e, sub( 0, add( 15, gain_tcx_e ) ) );
+#ifdef FIX_1781_SPECTRAL_GAPS
+    inv_gain2 = L_shr( inv_gain2, 2 ); /* 2 bits headroom */
+#else
     inv_gain2 = shr( inv_gain2, 2 ); /* 2 bits headroom */
+#endif
     inv_gain2_e = add( inv_gain2_e, 2 );
 
     /* find last nonzero line below iFirstLine, use it as start offset */
@@ -2571,7 +2588,11 @@ void tcx_noise_factor_ivas_fx(
         /* inv_gain2 *= (float)pow(tilt_factor, (float)i); */
         FOR( k = 0; k < i; k++ )
         {
+#ifdef FIX_1781_SPECTRAL_GAPS
+            inv_gain2 = L_shl( Mpy_32_32( inv_gain2, tilt_factor ), 1 );
+#else
             inv_gain2 = shl( mult( inv_gain2, tilt_factor ), 1 );
+#endif
         }
 
         i = add( i, 1 );
@@ -2639,7 +2660,11 @@ void tcx_noise_factor_ivas_fx(
 
     FOR( ; i < lowpassLine; i++ )
     {
+#ifdef FIX_1781_SPECTRAL_GAPS
+        inv_gain2 = L_shl( Mpy_32_32( inv_gain2, tilt_factor ), 1 );
+#else
         inv_gain2 = shl( mult( inv_gain2, tilt_factor ), 1 );
+#endif
 
         IF( sqQ[i] != 0 ) /* current line is not zero, so reset pointers */
         {
@@ -2707,8 +2732,12 @@ void tcx_noise_factor_ivas_fx(
                 win = add( win, 1 );
             }
             /* update segment sum: magnitudes scaled by smoothing function */
+#ifdef FIX_1781_SPECTRAL_GAPS
+            sqQ[i] = Mpy_32_32( imult3216( L_abs( x_orig[i] ), win ), inv_gain2 );
+#else
             sqQ[i] = Mpy_32_16_1( imult3216( L_abs( x_orig[i] ), win ), inv_gain2 );
             move32();
+#endif
             exp_spQ[i] = add( x_orig_e, inv_gain2_e );
             move16();
         }