diff --git a/library/pkcs7.c b/library/pkcs7.c
index cfe570a..3481cbd 100644
--- a/library/pkcs7.c
+++ b/library/pkcs7.c
@@ -9,6 +9,7 @@
 #include "mbedtls/asn1.h"
 #include "mbedtls/x509_crt.h"
 #include "mbedtls/x509_crl.h"
+#include "mbedtls/oid.h"
 #include "x509_oid.h"
 #include "mbedtls/error.h"