diff --git a/library/x509.c b/library/x509.c
index f0a9101..0cfcc53 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -831,6 +831,7 @@
     return( (int) ( size - n ) );
 }
 
+#if defined(MBEDTLS_X509_INFO)
 /*
  * Helper for writing signature algorithms
  */
@@ -875,6 +876,7 @@
 
     return( (int)( size - n ) );
 }
+#endif /* MBEDTLS_X509_INFO */
 
 /*
  * Helper for writing "RSA key size", "EC key size", etc