diff --git a/library/x509write_crt.c b/library/x509write_crt.c
index 184c90c..0c5e991 100644
--- a/library/x509write_crt.c
+++ b/library/x509write_crt.c
@@ -299,7 +299,7 @@
     /*
      * write MBEDTLS_ASN1_UTC_TIME if year < 2050 (2 bytes shorter)
      */
-    if( t[0] == '2' && t[1] == '0' && t[2] < '5' )
+    if( t[0] < '2' || ( t[0] == '2' && t[1] == '0' && t[2] < '5' ) )
     {
         MBEDTLS_ASN1_CHK_ADD( len, mbedtls_asn1_write_raw_buffer( p, start,
                                              (const unsigned char *) t + 2,