diff --git a/include/mbedtls/error.h b/include/mbedtls/error.h
index 9a8690d..d2d31a8 100644
--- a/include/mbedtls/error.h
+++ b/include/mbedtls/error.h
@@ -129,6 +129,7 @@
  *        Only used when invasive testing is enabled via MBEDTLS_TEST_HOOKS.
  */
 extern void (*mbedtls_test_hook_error_add)( int, int, const char *, int );
+extern void (*mbedtls_test_hook_value)( int test, const char * file, int line );
 #endif
 
 /**
diff --git a/include/mbedtls/mbedtls_config.h b/include/mbedtls/mbedtls_config.h
index a60db7e..1ab0ade 100644
--- a/include/mbedtls/mbedtls_config.h
+++ b/include/mbedtls/mbedtls_config.h
@@ -1683,7 +1683,7 @@
  *
  * Uncomment to enable invasive tests.
  */
-//#define MBEDTLS_TEST_HOOKS
+#define MBEDTLS_TEST_HOOKS
 
 /**
  * \def MBEDTLS_THREADING_ALT