diff --git a/library/base64.c b/library/base64.c
index 2b623b9..fa22e53 100644
--- a/library/base64.c
+++ b/library/base64.c
@@ -24,6 +24,7 @@
 #if defined(MBEDTLS_BASE64_C)
 
 #include "mbedtls/base64.h"
+#include "base64_internal.h"
 #include "constant_time_internal.h"
 
 #include <stdint.h>