diff --git a/include/mbedtls/base64.h b/include/mbedtls/base64.h
index 635be71..e82c270 100644
--- a/include/mbedtls/base64.h
+++ b/include/mbedtls/base64.h
@@ -87,6 +87,35 @@
 
 #endif /* MBEDTLS_SELF_TEST */
 
+#if defined(MBEDTLS_TEST_HOOKS)
+
+/** Given a value in the range 0..63, return the corresponding Base64 digit.
+ *
+ * The implementation assumes that letters are consecutive (e.g. ASCII
+ * but not EBCDIC).
+ *
+ * \param value     A value in the range 0..63.
+ *
+ * \return          A base64 digit converted from \p value.
+ */
+unsigned char mbedtls_ct_base64_enc_char(unsigned char value);
+
+/** Given a Base64 digit, return its value.
+ *
+ * If c is not a Base64 digit ('A'..'Z', 'a'..'z', '0'..'9', '+' or '/'),
+ * return -1.
+ *
+ * The implementation assumes that letters are consecutive (e.g. ASCII
+ * but not EBCDIC).
+ *
+ * \param c     A base64 digit.
+ *
+ * \return      The value of the base64 digit \p c.
+ */
+signed char mbedtls_ct_base64_dec_value(unsigned char c);
+
+#endif /* MBEDTLS_TEST_HOOKS */
+
 #ifdef __cplusplus
 }
 #endif