diff --git a/include/polarssl/bignum.h b/include/polarssl/bignum.h
index 681a1de..bfd4ce0 100644
--- a/include/polarssl/bignum.h
+++ b/include/polarssl/bignum.h
@@ -30,7 +30,11 @@
 #include <stdio.h>
 #include <string.h>
 
+#if !defined(POLARSSL_CONFIG_FILE)
 #include "config.h"
+#else
+#include POLARSSL_CONFIG_FILE
+#endif
 
 #if defined(_MSC_VER) && !defined(EFIX64) && !defined(EFI32)
 #include <basetsd.h>