diff --git a/lib_com/ivas_prot_fx.h b/lib_com/ivas_prot_fx.h
index 80bdda3c2e6fd4ce43204716ae9aa789eded3be5..1bdc334391239759cc906a3afe73dc709543a87a 100644
--- a/lib_com/ivas_prot_fx.h
+++ b/lib_com/ivas_prot_fx.h
@@ -4706,6 +4706,8 @@ Word32 dot_product_cholesky_fx(
     const Word32 *A, /* i  : Cholesky  matrix A              */
     const Word16 N   /* i  : vector & matrix size            */
 );
+
+#ifndef DOT_PROD_CHOLESKY_64BIT
 Word32 dot_product_cholesky_fixed(
     const Word32 *x, /* i  : vector x                        */
     const Word32 *A, /* i  : Cholesky  matrix A              */
@@ -4713,6 +4715,13 @@ Word32 dot_product_cholesky_fixed(
     const Word16 exp_x,
     const Word16 exp_A,
     Word16 *exp_sum );
+#else
+Word64 dot_product_cholesky_fixed(
+    const Word32 *x, /* i  : vector x                        */
+    const Word32 *A, /* i  : Cholesky  matrix A              */
+    const Word16 N   /* i  : vector & matrix size            */
+);
+#endif
 
 void v_mult_mat_fx(
     Word32 *y_fx, /* o  : the product x*A                         */
diff --git a/lib_com/ivas_tools.c b/lib_com/ivas_tools.c
index ec3c30723a14064891ab567e01b2f2dcdb4fdf9a..d557669289d85ac2da4113bda2f6fa5b210f5f23 100644
--- a/lib_com/ivas_tools.c
+++ b/lib_com/ivas_tools.c
@@ -606,6 +606,7 @@ void v_sub32_fx(
  * Therefore, S=A*A' where A is upper triangular matrix of size (m*m+m)/2 (zeros ommitted, column-wise)
  *---------------------------------------------------------------------*/
 
+#ifndef DOT_PROD_CHOLESKY_64BIT
 /*! r: the dot product x'*A*A'*x */
 Word32 dot_product_cholesky_fixed(
     const Word32 *x, /* i  : vector x                        Q31 - exp_x*/
@@ -642,6 +643,44 @@ Word32 dot_product_cholesky_fixed(
 
     return suma;
 }
+#else
+/*! r: the dot product x'*A*A'*x */
+Word64 dot_product_cholesky_fixed(
+    const Word32 *x, /* i  : vector x                        Q31 - exp_x*/
+    const Word32 *A, /* i  : Cholesky  matrix A              Q31 - exp_A*/
+    const Word16 N   /* i  : vector & matrix size            Q0*/
+)
+{
+    Word16 i, j;
+    Word64 suma, tmp_sum;
+    Word32 mul;
+    Word32 tmp;
+    const Word32 *pt_x, *pt_A;
+    pt_A = A;
+    suma = 0;
+    move64();
+
+    FOR( i = 0; i < N; i++ )
+    {
+        tmp_sum = 0;
+        move32();
+        pt_x = x;
+
+        FOR( j = 0; j <= i; j++ )
+        {
+            mul = Mpy_32_32( *pt_x++, *pt_A++ );
+            tmp_sum = W_add( tmp_sum, W_deposit32_l( mul ) );
+        }
+
+        tmp_sum = W_shr( tmp_sum, 4 ); // to make sure that the tmp_sum will not overflow
+        tmp = W_extract_l( tmp_sum );
+        suma = W_mac_32_32( suma, tmp, tmp );
+    }
+
+    return suma;
+}
+#endif
+
 void v_mult_mat_fixed(
     Word32 *y,       /* o  : the product x*A               Qx - guardbits*/
     const Word32 *x, /* i  : vector x                      Qx*/
diff --git a/lib_com/options.h b/lib_com/options.h
index d3570004d0ed950bbe6677bedf3af9376621fafa..59698f78e2d1313b399f15fb0b87c2761476ff07 100644
--- a/lib_com/options.h
+++ b/lib_com/options.h
@@ -173,4 +173,5 @@
 #define NONBE_FIX_1277_EVS_DTX_HIGH_RATE_THRESHOLD      /* VA/Eri: FLP issue 1277: Fix Mismatch in DTX high-rate threshold between EVS float and BASOP */
 #define NONBE_FIX_708_OSBA_BR_SWITCHING_CRASH   /* FhG: issue 708: fix crash in OSBA BR switching with long test vectors */
 //#define OPT_STEREO_32KBPS_V1                    /* Optimization made in stereo decoding path for 32kbps decoding */
+#define DOT_PROD_CHOLESKY_64BIT                 /* FhG: Issue 1323, optimized 64 bit implementation of dot_product_cholesky() */
 #endif
diff --git a/lib_enc/speech_music_classif_fx.c b/lib_enc/speech_music_classif_fx.c
index 295cff8a1a889597baf9340d513c08348b248002..0188ba45c608f4d9cb87e9dacab0f9f122e04a75 100644
--- a/lib_enc/speech_music_classif_fx.c
+++ b/lib_enc/speech_music_classif_fx.c
@@ -1683,10 +1683,16 @@ Word16 ivas_smc_gmm_fx(
     Word16 flag_odv;
     Word32 lps_fx, lpm_fx, lpn_fx;
     Word32 ps_fx[N_SMC_MIXTURES], pm_fx[N_SMC_MIXTURES], pn_fx[N_SMC_MIXTURES];
+#ifndef DOT_PROD_CHOLESKY_64BIT
     Word32 lprob_fx;
     Word16 lprob_exp = 0;
+#else
+    Word64 wprob_fx;
+#endif
     Word32 fvm_fx[N_PCA_COEF];
+#ifndef DOT_PROD_CHOLESKY_64BIT
     Word16 fvm_exp = 0;
+#endif
     Word32 sum_PS_fx, ps_diff_fx, ps_sta_fx;
     Word32 dlp_fx, wrelE_fx, wdrop_fx, wght_fx;
     Word32 wrise_fx;
@@ -2273,23 +2279,38 @@ Word16 ivas_smc_gmm_fx(
     FOR( m = 0; m < N_SMC_MIXTURES; m++ )
     {
         v_sub32_fx( FV_fx, &means_speech_fx[m * N_PCA_COEF], fvm_fx, N_PCA_COEF );
+#ifndef DOT_PROD_CHOLESKY_64BIT
         fvm_exp = sub( 31, Qfact_FV );
         lprob_exp = 0;
         move16();
         lprob_fx = dot_product_cholesky_fixed( fvm_fx, &prec_chol_speech_fx[m * ( N_PCA_COEF * N_PCA_COEF + N_PCA_COEF ) / 2], N_PCA_COEF, fvm_exp, 31 - 28, &lprob_exp );
         ps_fx[m] = L_sub( L_sub( L_add( log_weights_speech_compute[m], log_det_chol_speech_fx[m] ), L_shl( lprob_fx, sub( Q18 - 1, sub( Q31, lprob_exp ) ) ) ), HALF_N_PCA_COEF_LOG_P12_Q18 ); // Q18
+#else
+        wprob_fx = dot_product_cholesky_fixed( fvm_fx, &prec_chol_speech_fx[m * ( N_PCA_COEF * N_PCA_COEF + N_PCA_COEF ) / 2], N_PCA_COEF );                 // Q10
+        ps_fx[m] = L_sub( L_sub( L_add( log_weights_speech_compute[m], log_det_chol_speech_fx[m] ), W_shr( wprob_fx, Q10 ) ), HALF_N_PCA_COEF_LOG_P12_Q18 ); // Q18
+#endif
         move32();
         v_sub32_fx( FV_fx, &means_music_fx[m * N_PCA_COEF], fvm_fx, N_PCA_COEF );
+#ifndef DOT_PROD_CHOLESKY_64BIT
         lprob_exp = 0;
         move16();
         lprob_fx = dot_product_cholesky_fixed( fvm_fx, &prec_chol_music_fx[m * ( N_PCA_COEF * N_PCA_COEF + N_PCA_COEF ) / 2], N_PCA_COEF, fvm_exp, 31 - 28, &lprob_exp );
         pm_fx[m] = L_sub( L_sub( L_add( log_weights_music_compute[m], log_det_chol_music_fx[m] ), L_shl( lprob_fx, sub( Q18 - 1, sub( Q31, lprob_exp ) ) ) ), HALF_N_PCA_COEF_LOG_P12_Q18 ); // Q18
+#else
+        wprob_fx = dot_product_cholesky_fixed( fvm_fx, &prec_chol_music_fx[m * ( N_PCA_COEF * N_PCA_COEF + N_PCA_COEF ) / 2], N_PCA_COEF );                  // Q10
+        pm_fx[m] = L_sub( L_sub( L_add( log_weights_music_compute[m], log_det_chol_music_fx[m] ), W_shr( wprob_fx, Q10 ) ), HALF_N_PCA_COEF_LOG_P12_Q18 );   // Q18
+#endif
         move32();
         v_sub32_fx( FV_fx, &means_noise_fx[m * N_PCA_COEF], fvm_fx, N_PCA_COEF );
+#ifndef DOT_PROD_CHOLESKY_64BIT
         lprob_exp = 0;
         move16();
         lprob_fx = dot_product_cholesky_fixed( fvm_fx, &prec_chol_noise_fx[m * ( N_PCA_COEF * N_PCA_COEF + N_PCA_COEF ) / 2], N_PCA_COEF, fvm_exp, 31 - 28, &lprob_exp );
         pn_fx[m] = L_sub( L_sub( L_add( log_weights_noise_compute[m], log_det_chol_noise_fx[m] ), L_shl( lprob_fx, sub( Q18 - 1, sub( Q31, lprob_exp ) ) ) ), HALF_N_PCA_COEF_LOG_P12_Q18 ); // Q18
+#else
+        wprob_fx = dot_product_cholesky_fixed( fvm_fx, &prec_chol_noise_fx[m * ( N_PCA_COEF * N_PCA_COEF + N_PCA_COEF ) / 2], N_PCA_COEF );                  // Q10
+        pn_fx[m] = L_sub( L_sub( L_add( log_weights_noise_compute[m], log_det_chol_noise_fx[m] ), W_shr( wprob_fx, Q10 ) ), HALF_N_PCA_COEF_LOG_P12_Q18 );   // Q18
+#endif
         move32();
     }
 
@@ -2311,7 +2332,7 @@ Word16 ivas_smc_gmm_fx(
     hSpMusClas->lpn_fx = extract_l( L_shr( lpn_fx, 11 ) ); // Q7
     move16();
 #else
-    hSpMusClas->lpm_fx = extract_h( L_shl_sat( lpm_fx, 16 - 11 ) ); // Q7
+    hSpMusClas->lpm_fx = extract_h( L_shl_sat( lpm_fx, 16 - 11 ) );                                                                                          // Q7
     move16();
     hSpMusClas->lps_fx = extract_h( L_shl_sat( lps_fx, 16 - 11 ) ); // Q7
     move16();