diff --git a/lib_com/basop_util.c b/lib_com/basop_util.c
index 335f61c1e5d300df92356059d3064030f3db7351..3b1a0cf21666618d0ad0f75ddf6170d36cbc2d81 100644
--- a/lib_com/basop_util.c
+++ b/lib_com/basop_util.c
@@ -2720,25 +2720,59 @@ Word32 dotWord32_16_Mant32Exp( const Word32 *bufX32, /* i: 32-bit buffer with un
                                const Word16 *bufY16, /* i: 16-bit buffer quite right-aligned   */
                                Word16 bufY16_exp,    /* i: exponent of buffer bufY16           */
                                Word16 len,           /* i: buffer len to process               */
-                               Word16 *exp )         /* o: result exponent                     */
+#ifdef FIX_BASOP_1765_MASA1TC_CNG_MISMATCH
+                               Word16 *exp,           /* o: result exponent                     */
+                               const Word16 is_ivas ) /* i: flag indicating IVAS to maintain EVS BE */
+#else
+                               Word16 *exp ) /* o: result exponent                     */
+#endif
 {
     Word32 L_sum;
     Word16 shift, shift1, i;
 
 
-    shift = getScaleFactor32( bufX32, len );        /* current available headroom */
+    shift = getScaleFactor32( bufX32, len ); /* current available headroom */
+#ifdef FIX_BASOP_1765_MASA1TC_CNG_MISMATCH
+    IF( EQ_16( is_ivas, 1 ) )
+    {
+        shift = sub( shift, sub( 15, norm_s( len ) ) ); /* reduced required headroom  */
+    }
+    ELSE
+    {
+        shift = sub( shift, sub( 14, norm_s( len ) ) ); /* reduced required headroom  */
+    }
+#else
     shift = sub( shift, sub( 14, norm_s( len ) ) ); /* reduced required headroom  */
-    L_sum = 0;                                      /* Clear accu                 */
+#endif
+    L_sum = 0; /* Clear accu                 */
     move32();
     FOR( i = 0; i < len; i++ )
     {
+#ifdef FIX_BASOP_1765_MASA1TC_CNG_MISMATCH
+        IF( EQ_16( is_ivas, 1 ) )
+        {
+            L_sum = L_add( L_sum, Mpy_32_16_1( L_shl( bufX32[i], shift ), bufY16[i] ) );
+        }
+        ELSE
+        {
+            L_sum = L_mac0( L_sum, round_fx( L_shl( bufX32[i], shift ) ), bufY16[i] );
+        }
+#else
         L_sum = L_mac0( L_sum, round_fx( L_shl( bufX32[i], shift ) ), bufY16[i] );
+#endif
     }
     shift1 = norm_l( L_sum );
     L_sum = L_shl( L_sum, shift1 ); /* return value */
 
     shift = sub( add( bufX32_exp, bufY16_exp ), add( shift, shift1 ) );
+#ifdef FIX_BASOP_1765_MASA1TC_CNG_MISMATCH
+    IF( EQ_16( is_ivas, 0 ) )
+    {
+        shift = add( shift, 1 ); /* compensate for factor of 2 introduced by L_mac0 */
+    }
+#else
     shift = add( shift, 1 ); /* compensate for factor of 2 introduced by L_mac0 */
+#endif
     /* In case of NULL result, we want to have a 0 exponent too */
     if ( L_sum == 0 )
         shift = 0;
diff --git a/lib_com/basop_util.h b/lib_com/basop_util.h
index d5283043068cc058b96c41460f52b8c63d1189dc..19b0bb4aaf9535e1e737ce701b326825102876e8 100644
--- a/lib_com/basop_util.h
+++ b/lib_com/basop_util.h
@@ -864,7 +864,12 @@ Word32 dotWord32_16_Mant32Exp( const Word32 *bufX32, /* i: 32-bit buffer with un
                                const Word16 *bufY16, /* i: 16-bit buffer quite right-aligned   */
                                Word16 bufY16_exp,    /* i: exponent of buffer bufY16           */
                                Word16 len,           /* i: buffer len to process               */
-                               Word16 *exp );        /* o: result exponent                     */
+#ifdef FIX_BASOP_1765_MASA1TC_CNG_MISMATCH
+                               Word16 *exp,            /* o: result exponent                     */
+                               const Word16 is_ivas ); /* i: flag indicating IVAS to maintain EVS BE */
+#else
+                               Word16 *exp ); /* o: result exponent                     */
+#endif
 
 /*!**********************************************************************
    \brief   Converts linear factor or energy to Decibel
diff --git a/lib_com/options.h b/lib_com/options.h
index a1b758cfc563aca2adef722e54399cc2355c02f1..17408984580afc64e416c57dcba0a0185e93809c 100644
--- a/lib_com/options.h
+++ b/lib_com/options.h
@@ -106,6 +106,7 @@
 #define FIX_BASOP_2599_TCA_OVERFLOW                     /* VA: issue 2599, Fix TCA overflow */
 #define FIX_2588_MISSING_CONDITIONS                     /* VA: Proposed fix to 2588, addition of a condition in lsf_dec */
 #define FIX_BASOP_2442_MASA2TC_TO_MONO_AND_AMBI         /* Nokia: BASOP issue 2442: Increase accuracy of computations and add additional gain clamp for low energy decorrelated signal rendering. */
+#define FIX_BASOP_1765_MASA1TC_CNG_MISMATCH             /* Nokia: BASOP issue 1765: Improve accuracy of FD CNG noise estimation */
 
 /* ##################### End NON-BE switches ########################### */
 
diff --git a/lib_com/prot_fx.h b/lib_com/prot_fx.h
index 6458662e7e8522d0f2acdea2d7b0c5b6262879dc..f4d4c2c3b77b12e24a49df7fa239fa34ad89de29 100644
--- a/lib_com/prot_fx.h
+++ b/lib_com/prot_fx.h
@@ -6448,7 +6448,12 @@ void noisy_speech_detection_fx(
     HANDLE_FD_CNG_DEC hFdCngDec, /* i/o: FD_CNG structure            */
     const Word16 vad,            /* i  : VAD flag                    */
     const Word16 *syn,           /* i  : i   time-domain frame       */
+#ifdef FIX_BASOP_1765_MASA1TC_CNG_MISMATCH
+    const Word16 Q,
+    const Word16 is_ivas );
+#else
     const Word16 Q );
+#endif
 
 void generate_comfort_noise_dec_fx(
     Word32 **bufferReal, /* o   : matrix to real part of i   bands */
diff --git a/lib_dec/acelp_core_dec_fx.c b/lib_dec/acelp_core_dec_fx.c
index f0d79382c224c042ba3e8b1886230ece1e363735..cdb551e700ba6ca8315252aa7e7a4f28f6daebdf 100644
--- a/lib_dec/acelp_core_dec_fx.c
+++ b/lib_dec/acelp_core_dec_fx.c
@@ -1549,7 +1549,18 @@ ivas_error acelp_core_dec_fx(
             IF( st->idchan == 0 && ( st->flag_cna || ( EQ_16( st->cng_type, FD_CNG ) && LE_32( st->total_brate, ACELP_32k ) ) || ( st->cng_type == LP_CNG && LE_32( st->core_brate, SID_2k40 ) ) ) )
             {
                 /*Noisy speech detector*/
+#ifdef FIX_BASOP_1765_MASA1TC_CNG_MISMATCH
+                IF( NE_16( st->element_mode, EVS_MONO ) )
+                {
+                    noisy_speech_detection_fx( st->hFdCngDec, st->VAD, psyn_fx, st->Q_syn, 1 );
+                }
+                ELSE
+                {
+                    noisy_speech_detection_fx( st->hFdCngDec, st->VAD, psyn_fx, st->Q_syn, 0 );
+                }
+#else
                 noisy_speech_detection_fx( st->hFdCngDec, st->VAD, psyn_fx, st->Q_syn );
+#endif
 
                 st->hFdCngDec->hFdCngCom->likelihood_noisy_speech = mult_r( st->hFdCngDec->hFdCngCom->likelihood_noisy_speech, 32440 /*0.99 Q15*/ );
                 move16();
diff --git a/lib_dec/amr_wb_dec_fx.c b/lib_dec/amr_wb_dec_fx.c
index 1fdfe44a4d749b9fcab176963c3860d83364668f..fbe877f58c3d65c9cf93063dbe675d412873ac97 100644
--- a/lib_dec/amr_wb_dec_fx.c
+++ b/lib_dec/amr_wb_dec_fx.c
@@ -798,7 +798,11 @@ ivas_error amr_wb_dec_fx(
         move16();
 
         /*Noisy speech detector*/
+#ifdef FIX_BASOP_1765_MASA1TC_CNG_MISMATCH
+        noisy_speech_detection_fx( st_fx->hFdCngDec, st_fx->VAD, syn_fx, st_fx->Q_syn, 0 );
+#else
         noisy_speech_detection_fx( st_fx->hFdCngDec, st_fx->VAD, syn_fx, st_fx->Q_syn );
+#endif
 
         st_fx->hFdCngDec->hFdCngCom->likelihood_noisy_speech = mult_r( st_fx->hFdCngDec->hFdCngCom->likelihood_noisy_speech, 32440 /*0.99 Q15*/ );
         IF( st_fx->hFdCngDec->hFdCngCom->flag_noisy_speech != 0 )
diff --git a/lib_dec/evs_dec_fx.c b/lib_dec/evs_dec_fx.c
index add3a07c325f324e755746fcd5a0cadee4832812..85fde0949d609da0904f7a25015427f4a4023ab8 100644
--- a/lib_dec/evs_dec_fx.c
+++ b/lib_dec/evs_dec_fx.c
@@ -940,7 +940,11 @@ ivas_error evs_dec_fx(
                  * -------------------------------------------------------------- */
 
                 HANDLE_FD_CNG_DEC hFdCngDec = st_fx->hFdCngDec;
+#ifdef FIX_BASOP_1765_MASA1TC_CNG_MISMATCH
+                noisy_speech_detection_fx( st_fx->hFdCngDec, st_fx->VAD && EQ_16( st_fx->m_frame_type, ACTIVE_FRAME ), output_sp, 0, 0 );
+#else
                 noisy_speech_detection_fx( st_fx->hFdCngDec, st_fx->VAD && EQ_16( st_fx->m_frame_type, ACTIVE_FRAME ), output_sp, 0 );
+#endif
 
                 hFdCngDec->hFdCngCom->likelihood_noisy_speech = mult_r( hFdCngDec->hFdCngCom->likelihood_noisy_speech, 32440 /*0.99 Q15*/ ); /*Q15*/
                 if ( hFdCngDec->hFdCngCom->flag_noisy_speech != 0 )
diff --git a/lib_dec/fd_cng_dec_fx.c b/lib_dec/fd_cng_dec_fx.c
index dc24fc6f95d392b159d59871821adf309a494eed..6e44864a92f41cdd0aca3c89f9c980ace78f16a5 100644
--- a/lib_dec/fd_cng_dec_fx.c
+++ b/lib_dec/fd_cng_dec_fx.c
@@ -1481,7 +1481,11 @@ void perform_noise_estimation_dec_ivas_fx(
                     FOR( p = 0; p < npart; p++ )
                     {
                         temp = L_shl( msPeriodog[p], q_shift );
+#ifdef FIX_BASOP_1765_MASA1TC_CNG_MISMATCH
+                        msNoiseEst[p] = Madd_32_16( Mpy_32_16_r( msNoiseEst[p], add( sub( MAX_16, alpha ), 1 ) ), temp, alpha ); /*Q31 - hFdCngDec->msNoiseEst_exp*/ /* add one to alpha comp to get ONE_IN_Q15 - alpha */
+#else
                         msNoiseEst[p] = Madd_32_16( Mpy_32_16_r( msNoiseEst[p], sub( MAX_16, alpha ) ), temp, alpha ); /*Q31 - hFdCngDec->msNoiseEst_exp*/
+#endif
                         move32();
                     }
                 }
@@ -1681,7 +1685,11 @@ void perform_noise_estimation_dec_ivas_fx(
                             move16();
                         }
                     }
+#ifdef FIX_BASOP_1765_MASA1TC_CNG_MISMATCH
+                    *ptr_per = Madd_32_16( ( *ptr_per ), enr, add( sub( MAX_16, alpha ), 1 ) ); /*Q31 - enr_e*/ /* add one to alpha comp to get ONE_IN_Q15 - alpha */
+#else
                     *ptr_per = Madd_32_16( ( *ptr_per ), enr, sub( MAX_16, alpha ) ); /*Q31 - enr_e*/
+#endif
                     move32();
                     ptr_per++;
                 }
@@ -2093,7 +2101,12 @@ void noisy_speech_detection_fx(
     HANDLE_FD_CNG_DEC hFdCngDec, /* i/o: FD_CNG structure            */
     const Word16 vad,            /*Q0*/
     const Word16 *syn,           /* i  : input time-domain frame                  Q*/
+#ifdef FIX_BASOP_1765_MASA1TC_CNG_MISMATCH
+    const Word16 Q,
+    const Word16 is_ivas )
+#else
     const Word16 Q )
+#endif
 {
     Word16 i;
     Word32 tmp;
@@ -2109,7 +2122,11 @@ void noisy_speech_detection_fx(
 
     IF( vad == 0 )
     {
+#ifdef FIX_BASOP_1765_MASA1TC_CNG_MISMATCH
+        totalNoise = dotWord32_16_Mant32Exp( hFdCngDec->msNoiseEst, hFdCngDec->msNoiseEst_exp, hFdCngDec->psize_shaping_norm, hFdCngDec->psize_shaping_norm_exp, hFdCngDec->nFFTpart_shaping, &totalNoise_exp, is_ivas ); /*Q31 - totalNoise_exp*/
+#else
         totalNoise = dotWord32_16_Mant32Exp( hFdCngDec->msNoiseEst, hFdCngDec->msNoiseEst_exp, hFdCngDec->psize_shaping_norm, hFdCngDec->psize_shaping_norm_exp, hFdCngDec->nFFTpart_shaping, &totalNoise_exp ); /*Q31 - totalNoise_exp*/
+#endif
 
         /*
           - logTotalNoise is scaled by LD_DATA_SCALE+2
diff --git a/lib_dec/ivas_stereo_mdct_core_dec_fx.c b/lib_dec/ivas_stereo_mdct_core_dec_fx.c
index c64baefe63ce0e9cc2d37760a076376ce568428d..d04d30a06ea645ac8ced5a944bffd2f29a37a7f2 100644
--- a/lib_dec/ivas_stereo_mdct_core_dec_fx.c
+++ b/lib_dec/ivas_stereo_mdct_core_dec_fx.c
@@ -1023,7 +1023,11 @@ static void run_min_stats_fx(
             Copy_Scale_sig32_16( x[ch][0], x_fx_16, L_FRAME16k, 0 ); /* exp(x_e) */
 
             test();
+#ifdef FIX_BASOP_1765_MASA1TC_CNG_MISMATCH
+            noisy_speech_detection_fx( st->hFdCngDec, save_VAD[ch] && EQ_16( st->m_frame_type, ACTIVE_FRAME ), x_fx_16, sub( Q15, x_e[ch][0] ), 1 );
+#else
             noisy_speech_detection_fx( st->hFdCngDec, save_VAD[ch] && EQ_16( st->m_frame_type, ACTIVE_FRAME ), x_fx_16, sub( Q15, x_e[ch][0] ) );
+#endif
             st->hFdCngDec->hFdCngCom->likelihood_noisy_speech = add( mult_r( 32440 /* 0.99 in Q15 */, st->hFdCngDec->hFdCngCom->likelihood_noisy_speech ), mult_r( st->hFdCngDec->hFdCngCom->flag_noisy_speech, 328 /* 0.01 in Q15 */ ) ); /* Q15 */
             move16();
             st->lp_noise = st->hFdCngDec->lp_noise; /* Q9.23 */
diff --git a/lib_dec/ivas_tcx_core_dec_fx.c b/lib_dec/ivas_tcx_core_dec_fx.c
index 59932995308c88f81fc563d19779520b4a2cb3e8..cd03669c32038823979d0781515b0a72b1ecac51 100644
--- a/lib_dec/ivas_tcx_core_dec_fx.c
+++ b/lib_dec/ivas_tcx_core_dec_fx.c
@@ -837,7 +837,11 @@ void stereo_tcx_core_dec_fx(
     test();
     IF( st->hFdCngDec != NULL && ( EQ_32( st->sr_core, INT_FS_12k8 ) || EQ_32( st->sr_core, INT_FS_16k ) ) && LE_32( st->total_brate, MAX_ACELP_BRATE ) )
     {
+#ifdef FIX_BASOP_1765_MASA1TC_CNG_MISMATCH
+        noisy_speech_detection_fx( st->hFdCngDec, st->VAD && EQ_16( st->m_frame_type, ACTIVE_FRAME ), signal_out_fx, 0, 1 );
+#else
         noisy_speech_detection_fx( st->hFdCngDec, st->VAD && EQ_16( st->m_frame_type, ACTIVE_FRAME ), signal_out_fx, 0 );
+#endif
         st->hFdCngDec->hFdCngCom->likelihood_noisy_speech = add( mult_r( 32440 /* 0.99f in Q15 */, st->hFdCngDec->hFdCngCom->likelihood_noisy_speech ), mult_r( st->hFdCngDec->hFdCngCom->flag_noisy_speech, 328 /* 0.01f in Q15 */ ) ); /* Q15 */
         st->lp_noise = st->hFdCngDec->lp_noise;                                                                                                                                                                                          /* Q9.23 */
         move16();