diff --git a/ChangeLog b/ChangeLog
index 18116f7..2149ff2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -13,6 +13,10 @@
      Found by redplait #590
    * Add MBEDTLS_MPI_CHK to check for error value of mbedtls_mpi_fill_random.
      Reported and fix suggested by guidovranken in #740
+   * Fix a potential integer overflow in the version verification for DER
+     encoded X509 CRLs. The overflow would enable maliciously constructed CRLs
+     to bypass the version verification check. Found by Peng Li/Yueh-Hsun Lin,
+     KNOX Security, Samsung Research America
 
 = mbed TLS 2.1.8 branch released 2017-06-21
 
diff --git a/library/x509_crl.c b/library/x509_crl.c
index 3af10f6..a3ef8b4 100644
--- a/library/x509_crl.c
+++ b/library/x509_crl.c
@@ -352,14 +352,14 @@
         return( ret );
     }
 
-    crl->version++;
-
-    if( crl->version > 2 )
+    if( crl->version < 0 || crl->version > 1 )
     {
         mbedtls_x509_crl_free( crl );
         return( MBEDTLS_ERR_X509_UNKNOWN_VERSION );
     }
 
+    crl->version++;
+
     if( ( ret = mbedtls_x509_get_sig_alg( &crl->sig_oid, &sig_params1,
                                   &crl->sig_md, &crl->sig_pk,
                                   &crl->sig_opts ) ) != 0 )