diff --git a/lib/hx509/crypto_headers.h b/lib/hx509/crypto_headers.h
index d9690a0c8..d902472f7 100644
--- a/lib/hx509/crypto_headers.h
+++ b/lib/hx509/crypto_headers.h
@@ -21,6 +21,7 @@
 
 #ifndef BN_is_negative
 #define BN_set_negative(bn, flag) ((bn)->neg = (flag) ? 1 : 0)
+#define BN_is_negative(bn) ((bn)->neg != 0)
 #endif
 
 #else