diff --git a/include/mbedtls/x509_crt.h b/include/mbedtls/x509_crt.h
index 41b6bfe..383e484 100644
--- a/include/mbedtls/x509_crt.h
+++ b/include/mbedtls/x509_crt.h
@@ -120,6 +120,10 @@
 #define MBEDTLS_X509_RFC5280_MAX_SERIAL_LEN 32
 #define MBEDTLS_X509_RFC5280_UTC_TIME_LEN   15
 
+#if !defined( MBEDTLS_X509_MAX_FILE_PATH_LEN )
+#define MBEDTLS_X509_MAX_FILE_PATH_LEN 512
+#endif
+
 /**
  * Container for writing a certificate (CRT)
  */