diff --git a/library/bignum_mod.c b/library/bignum_mod.c
index 4303efefa..fa4831c7a 100644
--- a/library/bignum_mod.c
+++ b/library/bignum_mod.c
@@ -212,7 +212,8 @@ exit:
 int mbedtls_mpi_mod_read( mbedtls_mpi_mod_residue *r,
                           const mbedtls_mpi_mod_modulus *m,
                           const unsigned char *buf,
-                          size_t buflen )
+                          size_t buflen,
+                          mbedtls_mpi_mod_ext_rep ext_rep )
 {
     int ret = MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
 
@@ -223,7 +224,7 @@ int mbedtls_mpi_mod_read( mbedtls_mpi_mod_residue *r,
          r->limbs == 0 || m->limbs == 0 )
         goto cleanup;
 
-    ret = mbedtls_mpi_mod_raw_read( r->p, m, buf, buflen );
+    ret = mbedtls_mpi_mod_raw_read( r->p, m, buf, buflen, ext_rep );
 
     if( ret != 0 )
         goto cleanup;
@@ -240,7 +241,8 @@ cleanup:
 int mbedtls_mpi_mod_write( const mbedtls_mpi_mod_residue *r,
                            const mbedtls_mpi_mod_modulus *m,
                            unsigned char *buf,
-                           size_t buflen )
+                           size_t buflen,
+                           mbedtls_mpi_mod_ext_rep ext_rep )
 {
     int ret = MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
 
@@ -254,7 +256,7 @@ int mbedtls_mpi_mod_write( const mbedtls_mpi_mod_residue *r,
     if ( m->int_rep == MBEDTLS_MPI_MOD_REP_MONTGOMERY)
         ret = mbedtls_mpi_mod_raw_from_mont_rep( r->p, m );
 
-    ret = mbedtls_mpi_mod_raw_write( r->p, m, buf, buflen );
+    ret = mbedtls_mpi_mod_raw_write( r->p, m, buf, buflen, ext_rep );
 
 cleanup:
     return ( ret );
diff --git a/library/bignum_mod.h b/library/bignum_mod.h
index f0ce3c444..e6da15fbc 100644
--- a/library/bignum_mod.h
+++ b/library/bignum_mod.h
@@ -181,11 +181,12 @@ void mbedtls_mpi_mod_modulus_free( mbedtls_mpi_mod_modulus *m );
  * and will be padded to m->limbs). The data will be automatically converted
  * into the appropriate internal representation based on the value of `m->int_rep`.
  *
- * \param r      The address of the residue related to \p m. It must have as
- *               many limbs as the modulus \p m.
- * \param m      The address of the modulus.
- * \param buf    The input buffer to import from.
- * \param buflen The length in bytes of \p buf.
+ * \param r         The address of the residue related to \p m. It must have as
+ *                  many limbs as the modulus \p m.
+ * \param m         The address of the modulus.
+ * \param buf       The input buffer to import from.
+ * \param buflen    The length in bytes of \p buf.
+ * \param ext_rep   The endianness of the number in the input buffer.
  *
  * \return       \c 0 if successful.
  * \return       #MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL if \p X isn't
@@ -196,7 +197,8 @@ void mbedtls_mpi_mod_modulus_free( mbedtls_mpi_mod_modulus *m );
 int mbedtls_mpi_mod_read( mbedtls_mpi_mod_residue *r,
                           const mbedtls_mpi_mod_modulus *m,
                           const unsigned char *buf,
-                          size_t buflen );
+                          size_t buflen,
+                          mbedtls_mpi_mod_ext_rep ext_rep );
 
 /** Write residue data onto a buffer using public representation data.
  *
@@ -206,11 +208,12 @@ int mbedtls_mpi_mod_read( mbedtls_mpi_mod_residue *r,
  * converted from the appropriate internal representation based on the
  * value of `m->int_rep field`.
  *
- * \param r      The address of the residue related to \p m. It must have as
- *               many limbs as the modulus \p m.
- * \param m      The address of the modulus.
- * \param buf    The output buffer to export to.
- * \param buflen The length in bytes of \p buf.
+ * \param r         The address of the residue related to \p m. It must have as
+ *                  many limbs as the modulus \p m.
+ * \param m         The address of the modulus.
+ * \param buf       The output buffer to export to.
+ * \param buflen    The length in bytes of \p buf.
+ * \param ext_rep   The endianness in which the number should be written into the output buffer.
  *
  * \return       \c 0 if successful.
  * \return       #MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL if \p buf isn't
@@ -221,7 +224,8 @@ int mbedtls_mpi_mod_read( mbedtls_mpi_mod_residue *r,
 int mbedtls_mpi_mod_write( const mbedtls_mpi_mod_residue *r,
                            const mbedtls_mpi_mod_modulus *m,
                            unsigned char *buf,
-                           size_t buflen );
+                           size_t buflen,
+                           mbedtls_mpi_mod_ext_rep ext_rep );
 /* END MERGE SLOT 7 */
 
 /* BEGIN MERGE SLOT 8 */
diff --git a/tests/suites/test_suite_bignum_mod.function b/tests/suites/test_suite_bignum_mod.function
index 715a83998..5a75ebc3a 100644
--- a/tests/suites/test_suite_bignum_mod.function
+++ b/tests/suites/test_suite_bignum_mod.function
@@ -143,48 +143,59 @@ void mpi_mod_io_neg( )
     ASSERT_ALLOC( r_buff, buff_bytes );
     memset( r_buff, 0x1, 1 );
 
+    mbedtls_mpi_mod_ext_rep endian = MBEDTLS_MPI_MOD_EXT_REP_LE;
     TEST_EQUAL( 0, mbedtls_mpi_mod_modulus_setup( &m, N, n_limbs,
-                MBEDTLS_MPI_MOD_EXT_REP_LE, MBEDTLS_MPI_MOD_REP_MONTGOMERY ) );
+                endian, MBEDTLS_MPI_MOD_REP_MONTGOMERY ) );
 
     TEST_EQUAL( 0, mbedtls_mpi_mod_residue_setup( &r, &m, R , n_limbs ) );
 
     /* Pass for input_r < modulo */
-    TEST_EQUAL( 0, mbedtls_mpi_mod_read( &r, &m, r_buff, 1 ) );
+    TEST_EQUAL( 0, mbedtls_mpi_mod_read( &r, &m, r_buff, 1, endian ) );
 
     /* Pass for input_r == modulo -1 */
     memset( r_buff, 0xfd, buff_bytes );
-    TEST_EQUAL( 0, mbedtls_mpi_mod_read( &r, &m, r_buff, 1 ) );
+    TEST_EQUAL( 0, mbedtls_mpi_mod_read( &r, &m, r_buff, 1, endian ) );
 
     /* modulo->p == NULL || residue->p == NULL ( m2 has not been set-up ) */
-    TEST_EQUAL(MBEDTLS_ERR_MPI_BAD_INPUT_DATA, mbedtls_mpi_mod_read( &r, &m2, r_buff, 1 ) );
-    TEST_EQUAL(MBEDTLS_ERR_MPI_BAD_INPUT_DATA, mbedtls_mpi_mod_read( &rn, &m, r_buff, 1 ) );
-    TEST_EQUAL(MBEDTLS_ERR_MPI_BAD_INPUT_DATA, mbedtls_mpi_mod_write( &r, &m2, r_buff, 1 ) );
-    TEST_EQUAL(MBEDTLS_ERR_MPI_BAD_INPUT_DATA, mbedtls_mpi_mod_write( &rn, &m, r_buff, 1 ) );
+    TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
+                mbedtls_mpi_mod_read( &r, &m2, r_buff, 1, endian ) );
+    TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
+                mbedtls_mpi_mod_read( &rn, &m, r_buff, 1, endian ) );
+    TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
+                mbedtls_mpi_mod_write( &r, &m2, r_buff, 1, endian ) );
+    TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
+                mbedtls_mpi_mod_write( &rn, &m, r_buff, 1, endian ) );
 
     /* Fail for r_limbs < m->limbs */
     r.limbs = m.limbs - 1;
-    TEST_EQUAL(MBEDTLS_ERR_MPI_BAD_INPUT_DATA, mbedtls_mpi_mod_read( &r, &m, r_buff, 1 ) );
-    TEST_EQUAL(MBEDTLS_ERR_MPI_BAD_INPUT_DATA, mbedtls_mpi_mod_write( &rn, &m, r_buff, 1 ) );
+    TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
+                mbedtls_mpi_mod_read( &r, &m, r_buff, 1, endian ) );
+    TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
+                mbedtls_mpi_mod_write( &rn, &m, r_buff, 1, endian ) );
     r.limbs = r_limbs;
 
     /* Fail if input_r >= modulo m */
     /* input_r = modulo */
     memset( r_buff, 0xfe, buff_bytes );
-    TEST_EQUAL(MBEDTLS_ERR_MPI_BAD_INPUT_DATA, mbedtls_mpi_mod_read( &r, &m, r_buff, 1 ) );
+    TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
+                mbedtls_mpi_mod_read( &r, &m, r_buff, 1, endian ) );
 
     /* input_r > modulo */
     memset( r_buff, 0xff, buff_bytes );
-    TEST_EQUAL(MBEDTLS_ERR_MPI_BAD_INPUT_DATA, mbedtls_mpi_mod_read( &r, &m, r_buff, 1 ) );
+    TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
+                mbedtls_mpi_mod_read( &r, &m, r_buff, 1, endian ) );
 
     /* Data too large to fit */
-    TEST_EQUAL(MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL, mbedtls_mpi_mod_read( &r, &m, r_buff, buff_bytes ) );
+    TEST_EQUAL( MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL,
+                mbedtls_mpi_mod_read( &r, &m, r_buff, buff_bytes, endian ) );
 
     /* Read the two limbs input data into a larger modulus and residue */
     TEST_EQUAL( 0, mbedtls_mpi_mod_modulus_setup( &m2, N2, n2_limbs,
-                MBEDTLS_MPI_MOD_EXT_REP_LE, MBEDTLS_MPI_MOD_REP_MONTGOMERY ) );
+                endian, MBEDTLS_MPI_MOD_REP_MONTGOMERY ) );
     rn.p = R2;
     rn.limbs = r2_limbs;
-    TEST_EQUAL(MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL, mbedtls_mpi_mod_write( &rn, &m2, r_buff, 1 ) );
+    TEST_EQUAL( MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL,
+                mbedtls_mpi_mod_write( &rn, &m2, r_buff, 1, endian ) );
 
 exit:
     mbedtls_mpi_mod_modulus_free( &m );
@@ -198,7 +209,7 @@ exit:
 /* END_CASE */
 
 /* BEGIN_CASE */
-void mpi_mod_io( char * input_N, data_t * input_A, int iendian )
+void mpi_mod_io( char * input_N, data_t * input_A, int endian )
 {
     mbedtls_mpi_uint *N = NULL;
     mbedtls_mpi_uint *R = NULL;
@@ -221,15 +232,17 @@ void mpi_mod_io( char * input_N, data_t * input_A, int iendian )
 
     /* Init Structures */
     mbedtls_mpi_mod_modulus_init( &m );
-    TEST_EQUAL( 0, mbedtls_mpi_mod_modulus_setup( &m, N, n_limbs, iendian,
+    TEST_EQUAL( 0, mbedtls_mpi_mod_modulus_setup( &m, N, n_limbs, endian,
                 MBEDTLS_MPI_MOD_REP_MONTGOMERY ) );
 
     /* Enforcing p_limbs >= m->limbs */
-    TEST_EQUAL( 0, mbedtls_mpi_mod_residue_setup( &r, &m, R , n_limbs ) );
+    TEST_EQUAL( 0, mbedtls_mpi_mod_residue_setup( &r, &m, R, n_limbs ) );
 
-    TEST_EQUAL( 0, mbedtls_mpi_mod_read( &r, &m, input_A->x, input_A->len ) );
+    TEST_EQUAL( 0, mbedtls_mpi_mod_read( &r, &m, input_A->x, input_A->len,
+                                         endian ) );
 
-    TEST_EQUAL( 0,mbedtls_mpi_mod_write( &r, &m, r_buff, a_bytes ) );
+    TEST_EQUAL( 0, mbedtls_mpi_mod_write( &r, &m, r_buff, a_bytes,
+                                          endian ) );
 
     ASSERT_COMPARE( r_buff, a_bytes, input_A->x, a_bytes );
 exit: