diff --git a/library/x509.c b/library/x509.c
index 60e1cac..1b06e21 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -34,7 +34,11 @@
  *  http://www.itu.int/ITU-T/studygroups/com17/languages/X.690-0207.pdf
  */
 
+#if !defined(POLARSSL_CONFIG_FILE)
 #include "polarssl/config.h"
+#else
+#include POLARSSL_CONFIG_FILE
+#endif
 
 #if defined(POLARSSL_X509_USE_C)