diff --git a/tests/include/test/helpers.h b/tests/include/test/helpers.h
index fe3b787..6ec967e 100644
--- a/tests/include/test/helpers.h
+++ b/tests/include/test/helpers.h
@@ -298,12 +298,13 @@
  *                      of limbs is 0.
  * \param[out] plimbs   The address where the number of limbs will be stored.
  * \param[in] input     The test argument to read.
- *                      It is interpreted as a big-endian integer in base 256.
+ *                      It is interpreted as a hexadecimal representation
+ *                      of a non-negative integer.
  *
  * \return \c 0 on success, an \c MBEDTLS_ERR_MPI_xxx error code otherwise.
  */
 int mbedtls_test_read_mpi_core( mbedtls_mpi_uint **pX, size_t *plimbs,
-                                const data_t *input );
+                                const char *input );
 
 /** Read an MPI from a hexadecimal string.
  *
diff --git a/tests/src/helpers.c b/tests/src/helpers.c
index 557c13c..b7c8364 100644
--- a/tests/src/helpers.c
+++ b/tests/src/helpers.c
@@ -348,19 +348,46 @@
 #include "bignum_core.h"
 
 int mbedtls_test_read_mpi_core( mbedtls_mpi_uint **pX, size_t *plimbs,
-                                const data_t *input )
+                                const char *input )
 {
     /* Sanity check */
     if( *pX != NULL )
         return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
 
-    *plimbs = CHARS_TO_LIMBS( input->len );
+    size_t hex_len = strlen( input );
+    size_t byte_len = ( hex_len + 1 ) / 2;
+    *plimbs = CHARS_TO_LIMBS( byte_len );
     if( *plimbs == 0 )
         return( 0 );
+
     *pX = mbedtls_calloc( *plimbs, sizeof( **pX ) );
     if( *pX == NULL )
         return( MBEDTLS_ERR_MPI_ALLOC_FAILED );
-    return( mbedtls_mpi_core_read_be( *pX, *plimbs, input->x, input->len ) );
+
+    unsigned char *byte_start = ( unsigned char * ) *pX;
+    if( byte_len % sizeof( mbedtls_mpi_uint ) != 0 )
+    {
+        byte_start += sizeof( mbedtls_mpi_uint ) - byte_len % sizeof( mbedtls_mpi_uint );
+    }
+    if( ( hex_len & 1 ) != 0 )
+    {
+        /* mbedtls_test_unhexify wants an even number of hex digits */
+        TEST_ASSERT( ascii2uc( *input, byte_start ) == 0 );
+        ++byte_start;
+        ++input;
+        --byte_len;
+    }
+    TEST_ASSERT( mbedtls_test_unhexify( byte_start,
+                                        byte_len,
+                                        input,
+                                        &byte_len ) == 0 );
+
+    mbedtls_mpi_core_bigendian_to_host( *pX, *plimbs );
+    return( 0 );
+
+exit:
+    mbedtls_free( *pX );
+    return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
 }
 
 int mbedtls_test_read_mpi( mbedtls_mpi *X, const char *s )
diff --git a/tests/suites/test_suite_mpi.data b/tests/suites/test_suite_mpi.data
index be4c056..2a1e48f 100644
--- a/tests/suites/test_suite_mpi.data
+++ b/tests/suites/test_suite_mpi.data
@@ -595,13 +595,13 @@
 mpi_cmp_mpi:"-1230000000000000000":"0":-1
 
 mbedtls_mpi_core_lt_ct: x=y (1 limb)
-mpi_core_lt_ct:"02B5":"02B5":0
+mpi_core_lt_ct:"2B5":"2B5":0
 
 mbedtls_mpi_core_lt_ct: x>y (1 limb)
-mpi_core_lt_ct:"02B5":"02B4":0
+mpi_core_lt_ct:"2B5":"2B4":0
 
 mbedtls_mpi_core_lt_ct: x<y (1 limb)
-mpi_core_lt_ct:"02B5":"02B6":1
+mpi_core_lt_ct:"2B5":"2B6":1
 
 mbedtls_mpi_core_lt_ct: x=y (0 limbs)
 mpi_core_lt_ct:"":"":0
@@ -667,7 +667,7 @@
 mpi_core_lt_ct:"000000FF":"FFFFFFFF":1
 
 mbedtls_mpi_core_lt_ct: x<y, zero vs non-zero MS limb
-mpi_core_lt_ct:"00FFFFFFFFFFFFFFFF":"01FFFFFFFFFFFFFFFF":1
+mpi_core_lt_ct:"0FFFFFFFFFFFFFFFF":"1FFFFFFFFFFFFFFFF":1
 
 mbedtls_mpi_core_lt_ct: x>y, equal MS limbs
 mpi_core_lt_ct:"EEFFFFFFFFFFFFFFFF":"EEFFFFFFFFFFFFFFF1":0
diff --git a/tests/suites/test_suite_mpi.function b/tests/suites/test_suite_mpi.function
index d450197..2528b9c 100644
--- a/tests/suites/test_suite_mpi.function
+++ b/tests/suites/test_suite_mpi.function
@@ -728,7 +728,7 @@
 /* END_CASE */
 
 /* BEGIN_CASE */
-void mpi_core_lt_ct( data_t * input_X, data_t * input_Y, int exp_ret )
+void mpi_core_lt_ct( char *input_X, char *input_Y, int exp_ret )
 {
     mbedtls_mpi_uint *X = NULL;
     size_t X_limbs;