diff --git a/library/x509_crt.c b/library/x509_crt.c
index 99d3be2..490b524 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -961,8 +961,8 @@
             if( cb != NULL )
             {
                 ret = cb( p_ctx, crt, &extn_oid, is_critical, *p, end_ext_octet );
-                if( ret != 0 )
-                    return( MBEDTLS_ERR_X509_INVALID_EXTENSIONS + ret );
+                if( ret != 0 && is_critical )
+                    return( ret );
                 *p = end_ext_octet;
                 continue;
             }