diff --git a/include/mbedtls/base64.h b/include/mbedtls/base64.h
index f6f755913..8378589f3 100644
--- a/include/mbedtls/base64.h
+++ b/include/mbedtls/base64.h
@@ -87,16 +87,6 @@ int mbedtls_base64_self_test( int verbose );
 
 #endif /* MBEDTLS_SELF_TEST */
 
-#if defined(MBEDTLS_TEST_HOOKS)
-/* These functions are only exposed in testing configurations for testing
- * purposes and may change or disappear at any time. */
-unsigned char mbedtls_base64_mask_of_range( unsigned char low,
-                                            unsigned char high,
-                                            unsigned char c );
-unsigned char mbedtls_base64_enc_char( unsigned char val );
-signed char mbedtls_base64_dec_value( unsigned char c );
-#endif
-
 #ifdef __cplusplus
 }
 #endif
diff --git a/library/base64.c b/library/base64.c
index 96c94d1c6..085c71f3c 100644
--- a/library/base64.c
+++ b/library/base64.c
@@ -22,6 +22,7 @@
 #if defined(MBEDTLS_BASE64_C)
 
 #include "mbedtls/base64.h"
+#include "base64_invasive.h"
 
 #include <stdint.h>
 
diff --git a/library/base64_invasive.h b/library/base64_invasive.h
new file mode 100644
index 000000000..9e264719d
--- /dev/null
+++ b/library/base64_invasive.h
@@ -0,0 +1,55 @@
+/**
+ * \file base_invasive.h
+ *
+ * \brief Base64 module: interfaces for invasive testing only.
+ *
+ * The interfaces in this file are intended for testing purposes only.
+ * They SHOULD NOT be made available in library integrations except when
+ * building the library for testing.
+ */
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+#ifndef MBEDTLS_BASE64_INVASIVE_H
+#define MBEDTLS_BASE64_INVASIVE_H
+
+#include "common.h"
+
+#if defined(MBEDTLS_TEST_HOOKS)
+/* Return 0xff if low <= c <= high, 0 otherwise.
+ *
+ * Constant flow with respect to c.
+ */
+unsigned char mbedtls_base64_mask_of_range( unsigned char low,
+                                            unsigned char high,
+                                            unsigned char c );
+
+/* Given a value in the range 0..63, return the corresponding Base64 digit.
+ *
+ * Operates in constant time (no branches or memory access depending on val).
+ */
+unsigned char mbedtls_base64_enc_char( unsigned char val );
+
+/* Given a Base64 digit, return its value.
+ * If c is not a Base64 digit ('A'..'Z', 'a'..'z', '0'..'9', '+' or '/'),
+ * return -1.
+ *
+ * Operates in constant time (no branches or memory access depending on c).
+ */
+signed char mbedtls_base64_dec_value( unsigned char c );
+#endif /* MBEDTLS_TEST_HOOKS */
+
+#endif /* MBEDTLS_SSL_INVASIVE_H */
diff --git a/tests/suites/test_suite_base64.function b/tests/suites/test_suite_base64.function
index c0548956e..d0e116770 100644
--- a/tests/suites/test_suite_base64.function
+++ b/tests/suites/test_suite_base64.function
@@ -1,5 +1,6 @@
 /* BEGIN_HEADER */
 #include "mbedtls/base64.h"
+#include "base64_invasive.h"
 #include <test/constant_flow.h>
 /* END_HEADER */