diff --git a/library/bignum.c b/library/bignum.c
index 74f10af8d..fadd9e9cc 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -30,6 +30,7 @@
 #include "mbedtls/platform_util.h"
 #include "mbedtls/error.h"
 #include "constant_time_internal.h"
+#include "bignum_internal.h"
 
 #include <limits.h>
 #include <string.h>