diff --git a/c/reciprocal_to_normal.c b/c/reciprocal_to_normal.c
index bf30e175..c3f39bef 100644
--- a/c/reciprocal_to_normal.c
+++ b/c/reciprocal_to_normal.c
@@ -34,6 +34,11 @@
 
 #include "reciprocal_to_normal.h"
 
+#if defined(MKL_LAPACKE) || defined(SCIPY_MKL_H)
+#include <mkl_cblas.h>
+#else
+#include <cblas.h>
+#endif
 #include <math.h>
 #include <stdlib.h>
 
@@ -49,7 +54,11 @@ static double get_fc3_sum(const lapack_complex_double *e0,
                           const lapack_complex_double *e2,
                           const lapack_complex_double *fc3_reciprocal,
                           const long num_band);
-
+static double get_fc3_sum_blas(const lapack_complex_double *e0,
+                               const lapack_complex_double *e1,
+                               const lapack_complex_double *e2,
+                               const lapack_complex_double *fc3_reciprocal,
+                               const long num_band);
 void reciprocal_to_normal_squared(
     double *fc3_normal_squared, const long (*g_pos)[4], const long num_g_pos,
     const lapack_complex_double *fc3_reciprocal, const double *freqs0,
@@ -189,3 +198,40 @@ static double get_fc3_sum(const lapack_complex_double *e0,
     e_12_cache = NULL;
     return (sum_real * sum_real + sum_imag * sum_imag);
 }
+
+static double get_fc3_sum_blas(const lapack_complex_double *e0,
+                               const lapack_complex_double *e1,
+                               const lapack_complex_double *e2,
+                               const lapack_complex_double *fc3_reciprocal,
+                               const long num_band) {
+    long i, j;
+    lapack_complex_double *fc3_e12, *e_12, zero, one, retval;
+    const lapack_complex_double *fc3_i;
+
+    e_12 = (lapack_complex_double *)malloc(sizeof(lapack_complex_double) *
+                                           num_band * num_band);
+    fc3_e12 = (lapack_complex_double *)malloc(sizeof(lapack_complex_double) *
+                                              num_band);
+    zero = lapack_make_complex_double(0, 0);
+    one = lapack_make_complex_double(1, 0);
+
+    for (i = 0; i < num_band; i++) {
+        cblas_zcopy(num_band, e2, 1, e_12 + i * num_band, 1);
+        cblas_zscal(num_band, e1 + i, e_12 + i * num_band, 1);
+    }
+
+    cblas_zgemv(CblasRowMajor, CblasNoTrans, num_band, num_band * num_band,
+                &one, fc3_reciprocal, num_band * num_band, e_12, 1, &zero,
+                fc3_e12, 1);
+    cblas_zdotu_sub(num_band, e0, 1, fc3_e12, 1, &retval);
+
+    free(e_12);
+    e_12 = NULL;
+    free(fc3_e12);
+    fc3_e12 = NULL;
+
+    return lapack_complex_double_real(retval) *
+               lapack_complex_double_real(retval) +
+           lapack_complex_double_imag(retval) *
+               lapack_complex_double_imag(retval);
+}