diff --git a/tests/include/test/helpers.h b/tests/include/test/helpers.h
index 5f9bde6..b64bfcb 100644
--- a/tests/include/test/helpers.h
+++ b/tests/include/test/helpers.h
@@ -216,6 +216,17 @@
                           int len );
 
 /**
+ * \brief Convert hexadecimal digit to an integer.
+ *
+ * \param c        The digit to convert (`'0'` to `'9'`, `'A'` to `'F'` or
+ *                 `'a'` to `'f'`).
+ * \param[out] uc  On success, the value of the digit (0 to 15).
+ *
+ * \return         0 on success, -1 if \p c is not a hexadecimal digit.
+ */
+int mbedtls_test_ascii2uc(const char c, unsigned char *uc);
+
+/**
  * Allocate and zeroize a buffer.
  *
  * If the size if zero, a pointer to a zeroized 1-byte buffer is returned.
@@ -269,60 +280,4 @@
                                  const char *file, int line);
 #endif
 
-#if defined(MBEDTLS_BIGNUM_C)
-/** Allocate and populate a core MPI from a test case argument.
- *
- * This function allocates exactly as many limbs as necessary to fit
- * the length of the input. In other words, it preserves leading zeros.
- *
- * The limb array is allocated with mbedtls_calloc() and must later be
- * freed with mbedtls_free().
- *
- * \param[in,out] pX    The address where a pointer to the allocated limb
- *                      array will be stored.
- *                      \c *pX must be null on entry.
- *                      On exit, \c *pX is null on error or if the number
- *                      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 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 char *input );
-
-/** Read an MPI from a hexadecimal string.
- *
- * Like mbedtls_mpi_read_string(), but with tighter guarantees around
- * edge cases.
- *
- * - This function guarantees that if \p s begins with '-' then the sign
- *   bit of the result will be negative, even if the value is 0.
- *   When this function encounters such a "negative 0", it
- *   increments #mbedtls_test_case_uses_negative_0.
- * - The size of the result is exactly the minimum number of limbs needed
- *   to fit the digits in the input. In particular, this function constructs
- *   a bignum with 0 limbs for an empty string, and a bignum with leading 0
- *   limbs if the string has sufficiently many leading 0 digits.
- *   This is important so that the "0 (null)" and "0 (1 limb)" and
- *   "leading zeros" test cases do what they claim.
- *
- * \param[out] X        The MPI object to populate. It must be initialized.
- * \param[in] s         The null-terminated hexadecimal string to read from.
- *
- * \return \c 0 on success, an \c MBEDTLS_ERR_MPI_xxx error code otherwise.
- */
-int mbedtls_test_read_mpi( mbedtls_mpi *X, const char *s );
-
-/** Nonzero if the current test case had an input parsed with
- * mbedtls_test_read_mpi() that is a negative 0 (`"-"`, `"-0"`, `"-00"`, etc.,
- * constructing a result with the sign bit set to -1 and the value being
- * all-limbs-0, which is not a valid representation in #mbedtls_mpi but is
- * tested for robustness).
- */
-extern unsigned mbedtls_test_case_uses_negative_0;
-#endif /* MBEDTLS_BIGNUM_C */
-
 #endif /* TEST_HELPERS_H */