diff --git a/ChangeLog b/ChangeLog
index e847b65bc..90c6e6bcf 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -20,6 +20,10 @@ Bugfix
    * Fix a potential integer overflow in the version verification for DER
      encoded X509 certificates. The overflow would enable maliciously
      constructed certificates to bypass the certificate verification check.
+   * Fix potential integer overflow in the version verification for DER
+     encoded X509 CSRs. The overflow would enable maliciously constructed CSRs
+     to bypass the version verification check. Found by Peng Li/Yueh-Hsun Lin,
+     KNOX Security, Samsung Research America
 
 = mbed TLS 1.3.20 branch released 2017-06-21
 
diff --git a/library/x509_csr.c b/library/x509_csr.c
index 9bdfe884f..b3c8f29b7 100644
--- a/library/x509_csr.c
+++ b/library/x509_csr.c
@@ -169,14 +169,14 @@ int x509_csr_parse_der( x509_csr *csr,
         return( ret );
     }
 
-    csr->version++;
-
-    if( csr->version != 1 )
+    if( csr->version != 0 )
     {
         x509_csr_free( csr );
         return( POLARSSL_ERR_X509_UNKNOWN_VERSION );
     }
 
+    csr->version++;
+
     /*
      *  subject               Name
      */