diff --git a/library/x509write_crt.c b/library/x509write_crt.c
index 5462e83..aaffd14 100644
--- a/library/x509write_crt.c
+++ b/library/x509write_crt.c
@@ -203,7 +203,7 @@
     return(
         mbedtls_x509write_crt_set_extension( ctx, MBEDTLS_OID_BASIC_CONSTRAINTS,
                              MBEDTLS_OID_SIZE( MBEDTLS_OID_BASIC_CONSTRAINTS ),
-                             0, buf + sizeof(buf) - len, len ) );
+                             is_ca, buf + sizeof(buf) - len, len ) );
 }
 
 #if defined(MBEDTLS_SHA1_C)