diff --git a/library/constant_time_internal.h b/library/constant_time_internal.h
index c4a32c7..4ca3925 100644
--- a/library/constant_time_internal.h
+++ b/library/constant_time_internal.h
@@ -185,35 +185,6 @@
 
 #endif /* MBEDTLS_BIGNUM_C */
 
-#if defined(MBEDTLS_BASE64_C)
-
-/** 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_BASE64_C */
-
 #if defined(MBEDTLS_SSL_SOME_SUITES_USE_MAC)
 
 /** Conditional memcpy without branches.
@@ -360,4 +331,16 @@
 
 #endif /* MBEDTLS_PKCS1_V15 && MBEDTLS_RSA_C && ! MBEDTLS_RSA_ALT */
 
+#if defined(MBEDTLS_BASE64_C)
+
+/* Return 0xff if low <= c <= high, 0 otherwise.
+ *
+ * Constant flow with respect to c.
+ */
+unsigned char mbedtls_ct_uchar_mask_of_range(unsigned char low,
+                                             unsigned char high,
+                                             unsigned char c);
+
+#endif /* MBEDTLS_BASE64_C */
+
 #endif /* MBEDTLS_CONSTANT_TIME_INTERNAL_H */