diff --git a/tests/suites/test_suite_bignum_mod.data b/tests/suites/test_suite_bignum_mod.data
index 8579becfa..2ea4a5833 100644
--- a/tests/suites/test_suite_bignum_mod.data
+++ b/tests/suites/test_suite_bignum_mod.data
@@ -57,19 +57,19 @@ Test mbedtls_mpi_residue_setup #8 r > m
 mpi_residue_setup:"fe":"ff":-4
 
 Test mbedtls_mpi_mod_io_neg #1 input_r < modulo m
-mpi_mod_io_neg:"fe":"01":"fd":0
+mpi_mod_io_neg:"fe":"fd":0
 
 Test mbedtls_mpi_mod_io_neg #2  input_r == modulo m
-mpi_mod_io_neg:"fe":"01":"fe":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
+mpi_mod_io_neg:"fe":"fe":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
 Test mbedtls_mpi_mod_io_neg #3  input_r > modulo m
-mpi_mod_io_neg:"fe":"01":"ff":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
+mpi_mod_io_neg:"fe":"ff":MBEDTLS_ERR_MPI_BAD_INPUT_DATA
 
 Test mbedtls_mpi_mod_io_neg #4  input_r too large to fit
-mpi_mod_io_neg:"fe":"01":"ffffffffffffffffff":MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL
+mpi_mod_io_neg:"fe":"ffffffffffffffffff":MBEDTLS_ERR_MPI_BUFFER_TOO_SMALL
 
 Test mbedtls_mpi_mod_io_neg #5  Sucesfull read / output buffer too small
-mpi_mod_io_neg:"7ffffffffffffffffffffffffffffff1":"7ffffffffffffffffffffffffffffff0":"ffff":0
+mpi_mod_io_neg:"7ffffffffffffffffffffffffffffff1":"ffff":0
 
 Test mbedtls_mpi_mod_io #1 N: "11" A: "119".
 mpi_mod_io:"000000000000000b":"0000000000000000":MBEDTLS_MPI_MOD_EXT_REP_BE
diff --git a/tests/suites/test_suite_bignum_mod.function b/tests/suites/test_suite_bignum_mod.function
index 1d6b850b5..6a70e7287 100644
--- a/tests/suites/test_suite_bignum_mod.function
+++ b/tests/suites/test_suite_bignum_mod.function
@@ -114,11 +114,10 @@ exit:
 /* END_CASE */
 
 /* BEGIN_CASE */
-void mpi_mod_io_neg( char * input_N, char * input_R, data_t * buf, int ret )
+void mpi_mod_io_neg( char * input_N, data_t * buf, int ret )
 {
     mbedtls_mpi_uint *N = NULL;
     mbedtls_mpi_uint *R = NULL;
-    size_t n_limbs, r_limbs;
 
     mbedtls_mpi_mod_modulus m;
     mbedtls_mpi_mod_residue r;
@@ -127,8 +126,10 @@ void mpi_mod_io_neg( char * input_N, char * input_R, data_t * buf, int ret )
 
     mbedtls_mpi_mod_modulus_init( &m );
 
+    size_t n_limbs;
     TEST_EQUAL( 0, mbedtls_test_read_mpi_core( &N, &n_limbs, input_N ) );
-    TEST_EQUAL( 0, mbedtls_test_read_mpi_core( &R, &r_limbs, input_R ) );
+    size_t r_limbs = n_limbs;
+    ASSERT_ALLOC( R, r_limbs );
 
     /* modulo->p == NULL || residue->p == NULL ( m has not been set-up ) */
     TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,
@@ -139,7 +140,7 @@ void mpi_mod_io_neg( char * input_N, char * input_R, data_t * buf, int ret )
 
     TEST_EQUAL( 0, mbedtls_mpi_mod_modulus_setup( &m, N, n_limbs,
                 MBEDTLS_MPI_MOD_REP_MONTGOMERY ) );
-    TEST_EQUAL( 0, mbedtls_mpi_mod_residue_setup( &r, &m, R , n_limbs ) );
+    TEST_EQUAL( 0, mbedtls_mpi_mod_residue_setup( &r, &m, R , r_limbs ) );
 
     /* modulo->p == NULL || residue->p == NULL ( m has been set-up ) */
     TEST_EQUAL( MBEDTLS_ERR_MPI_BAD_INPUT_DATA,