diff --git a/library/bignum_mod.c b/library/bignum_mod.c
index 770e633..c10fb2e 100644
--- a/library/bignum_mod.c
+++ b/library/bignum_mod.c
@@ -210,8 +210,8 @@
 
 /* BEGIN MERGE SLOT 7 */
 int mbedtls_mpi_mod_read( mbedtls_mpi_mod_residue *r,
-                          mbedtls_mpi_mod_modulus *m,
-                          unsigned char *buf,
+                          const mbedtls_mpi_mod_modulus *m,
+                          const unsigned char *buf,
                           size_t buflen )
 {
     int ret = MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
@@ -219,7 +219,7 @@
     if ( r == NULL || m == NULL )
         goto cleanup;
 
-    if ( r->p == NULL || m->p == NULL || r->limbs > m->limbs ||\
+    if ( r->p == NULL || m->p == NULL || r->limbs > m->limbs ||
          r->limbs == 0 || m->limbs == 0 )
         goto cleanup;
 
@@ -228,6 +228,8 @@
     if( ret != 0 )
         goto cleanup;
 
+    r->limbs = m->limbs;
+
     if (m->int_rep == MBEDTLS_MPI_MOD_REP_MONTGOMERY)
        ret = mbedtls_mpi_mod_raw_to_mont_rep(r->p, m);
 
@@ -235,8 +237,8 @@
     return ( ret );
 }
 
-int mbedtls_mpi_mod_write( mbedtls_mpi_mod_residue *r,
-                           mbedtls_mpi_mod_modulus *m,
+int mbedtls_mpi_mod_write( const mbedtls_mpi_mod_residue *r,
+                           const mbedtls_mpi_mod_modulus *m,
                            unsigned char *buf,
                            size_t buflen )
 {
@@ -245,7 +247,7 @@
     if ( r == NULL || m == NULL )
         goto cleanup;
 
-    if ( r->p == NULL || m->p == NULL || r->limbs > m->limbs ||\
+    if ( r->p == NULL || m->p == NULL || r->limbs > m->limbs ||
          r->limbs == 0 || m->limbs == 0 )
         goto cleanup;
 
diff --git a/library/bignum_mod.h b/library/bignum_mod.h
index 4a01dfc..f0ce3c4 100644
--- a/library/bignum_mod.h
+++ b/library/bignum_mod.h
@@ -177,8 +177,9 @@
 /** Read public representation data stored in a buffer into a residue structure.
  *
  * The `mbedtls_mpi_mod_residue` and `mbedtls_mpi_mod_modulus` structures must
- * be compatible. The data will be automatically converted into the appropriate
- * representation based on the value of `m->int_rep field`.
+ * be compatible (Data in public representation is assumed to be in the m->ext_rep
+ * 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.
@@ -193,15 +194,17 @@
  *               of \p m is invalid or \p X is not less than \p m.
  */
 int mbedtls_mpi_mod_read( mbedtls_mpi_mod_residue *r,
-                          mbedtls_mpi_mod_modulus *m,
-                          unsigned char *buf,
+                          const mbedtls_mpi_mod_modulus *m,
+                          const unsigned char *buf,
                           size_t buflen );
 
 /** Write residue data onto a buffer using public representation data.
  *
  * The `mbedtls_mpi_mod_residue` and `mbedtls_mpi_mod_modulus` structures must
- * be compatible. The data will be automatically converted into the appropriate
- * representation based on the value of `m->int_rep field`.
+ * be compatible (Data will be exported onto the bufer using the m->ext_rep
+ * and will be read as of m->limbs length).The data will be automatically
+ * 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.
@@ -215,8 +218,8 @@
  * \return       #MBEDTLS_ERR_MPI_BAD_INPUT_DATA if the external representation
  *               of \p m is invalid.
  */
-int mbedtls_mpi_mod_write( mbedtls_mpi_mod_residue *r,
-                           mbedtls_mpi_mod_modulus *m,
+int mbedtls_mpi_mod_write( const mbedtls_mpi_mod_residue *r,
+                           const mbedtls_mpi_mod_modulus *m,
                            unsigned char *buf,
                            size_t buflen );
 /* END MERGE SLOT 7 */
diff --git a/tests/suites/test_suite_bignum_mod.function b/tests/suites/test_suite_bignum_mod.function
index e4d7b41..715a839 100644
--- a/tests/suites/test_suite_bignum_mod.function
+++ b/tests/suites/test_suite_bignum_mod.function
@@ -110,13 +110,6 @@
 /* BEGIN_CASE */
 void mpi_mod_io_neg( )
 {
-    #define IO_ZERO        0
-    #define IO_ONE         1
-    #define IO_MIN1        2
-    #define IO_MAX         3
-    #define IO_2LIMBS_MIN1 4
-    #define IO_2LIMBS      5
-
     mbedtls_mpi_uint *N = NULL;
     mbedtls_mpi_uint *R = NULL;
     mbedtls_mpi_uint *N2 = NULL;
@@ -130,15 +123,18 @@
     mbedtls_mpi_mod_modulus m2;
     mbedtls_mpi_mod_residue rn = { NULL, 0 };
 
-    const char * s_data[ 6 ] = { "00", "01", "fe", "ff",
-                                 "7ffffffffffffffff0" ,"7ffffffffffffffff1" };
+    const char *hex_residue_single = "01";
+    const char *hex_modulus_single = "fe";
+    const char *hex_residue_multi = "7ffffffffffffffffffffffffffffff0";
+    const char *hex_modulus_multi = "7ffffffffffffffffffffffffffffff1";
+
     const size_t buff_bytes = 1024;
 
     /* Allocate the memory for intermediate data structures */
-    TEST_EQUAL( 0, mbedtls_test_read_mpi_core( &N, &n_limbs, s_data[ IO_MIN1 ] ) );
-    TEST_EQUAL( 0, mbedtls_test_read_mpi_core( &R, &r_limbs, s_data[ IO_ONE ] ) );
-    TEST_EQUAL( 0, mbedtls_test_read_mpi_core( &N2, &n2_limbs, s_data[ IO_2LIMBS ] ) );
-    TEST_EQUAL( 0, mbedtls_test_read_mpi_core( &R2, &r2_limbs, s_data[ IO_2LIMBS_MIN1 ] ) );
+    TEST_EQUAL( 0, mbedtls_test_read_mpi_core( &N, &n_limbs, hex_modulus_single ) );
+    TEST_EQUAL( 0, mbedtls_test_read_mpi_core( &R, &r_limbs, hex_residue_single ) );
+    TEST_EQUAL( 0, mbedtls_test_read_mpi_core( &N2, &n2_limbs, hex_modulus_multi ) );
+    TEST_EQUAL( 0, mbedtls_test_read_mpi_core( &R2, &r2_limbs, hex_residue_multi ) );
 
     mbedtls_mpi_mod_modulus_init( &m );
     mbedtls_mpi_mod_modulus_init( &m2 );
@@ -155,7 +151,7 @@
     /* Pass for input_r < modulo */
     TEST_EQUAL( 0, mbedtls_mpi_mod_read( &r, &m, r_buff, 1 ) );
 
-    /* input_r == modulo -1 */
+    /* Pass for input_r == modulo -1 */
     memset( r_buff, 0xfd, buff_bytes );
     TEST_EQUAL( 0, mbedtls_mpi_mod_read( &r, &m, r_buff, 1 ) );
 
@@ -198,13 +194,6 @@
     mbedtls_free( N2 );
     mbedtls_free( R2 );
     mbedtls_free( r_buff );
-
-    #undef IO_ZERO
-    #undef IO_ONE
-    #undef IO_MIN1
-    #undef IO_MAX
-    #undef IO_2LIMBS_MIN1
-    #undef IO_2LIMBS
 }
 /* END_CASE */