diff --git a/ChangeLog b/ChangeLog
index cdd8257..4578146 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -9,6 +9,11 @@
    * Fix unused variable/function compilation warnings in pem.c and x509_csr.c
      that are reported when building mbed TLS with a config.h that does not
      define MBEDTLS_PEM_PARSE_C. Found by omnium21. #562
+   * Fix incorrect renegotiation condition in ssl_check_ctr_renegotiate() that
+     would compare 64 bits of the record counter instead of 48 bits as indicated
+     in RFC 6347 Section 4.3.1. This could cause the execution of the
+     renegotiation routines at unexpected times when the protocol is DTLS. Found
+     by wariua. #687
 
 = mbed TLS 2.1.6 branch released 2016-10-17
 
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index fa7fbda..fa9d48c 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -1946,7 +1946,7 @@
 
 /**
  * \brief          Set record counter threshold for periodic renegotiation.
- *                 (Default: 2^64 - 256.)
+ *                 (Default: 2^48 - 1)
  *
  *                 Renegotiation is automatically triggered when a record
  *                 counter (outgoing or ingoing) crosses the defined
@@ -1957,9 +1957,11 @@
  *                 Lower values can be used to enforce policies such as "keys
  *                 must be refreshed every N packets with cipher X".
  *
+ * \note           When the transport is set to MBEDTLS_SSL_TRANSPORT_DATAGRAM,
+ *                 the maximum renegotiation period is 2^48 - 1.
+ *
  * \param conf     SSL configuration
  * \param period   The threshold value: a big-endian 64-bit number.
- *                 Set to 2^64 - 1 to disable periodic renegotiation
  */
 void mbedtls_ssl_conf_renegotiation_period( mbedtls_ssl_config *conf,
                                    const unsigned char period[8] );
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index c455625..43efe0c 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -6380,6 +6380,10 @@
  */
 static int ssl_check_ctr_renegotiate( mbedtls_ssl_context *ssl )
 {
+    size_t ep_len = ssl_ep_len( ssl );
+    int in_ctr_cmp;
+    int out_ctr_cmp;
+
     if( ssl->state != MBEDTLS_SSL_HANDSHAKE_OVER ||
         ssl->renego_status == MBEDTLS_SSL_RENEGOTIATION_PENDING ||
         ssl->conf->disable_renegotiation == MBEDTLS_SSL_RENEGOTIATION_DISABLED )
@@ -6387,8 +6391,12 @@
         return( 0 );
     }
 
-    if( memcmp( ssl->in_ctr,  ssl->conf->renego_period, 8 ) <= 0 &&
-        memcmp( ssl->out_ctr, ssl->conf->renego_period, 8 ) <= 0 )
+    in_ctr_cmp = memcmp( ssl->in_ctr + ep_len,
+                        ssl->conf->renego_period + ep_len, 8 - ep_len );
+    out_ctr_cmp = memcmp( ssl->out_ctr + ep_len,
+                          ssl->conf->renego_period + ep_len, 8 - ep_len );
+
+    if( in_ctr_cmp <= 0 && out_ctr_cmp <= 0 )
     {
         return( 0 );
     }
@@ -7120,8 +7128,8 @@
 
 #if defined(MBEDTLS_SSL_RENEGOTIATION)
     conf->renego_max_records = MBEDTLS_SSL_RENEGO_MAX_RECORDS_DEFAULT;
-    memset( conf->renego_period, 0xFF, 7 );
-    conf->renego_period[7] = 0x00;
+    memset( conf->renego_period,     0x00, 2 );
+    memset( conf->renego_period + 2, 0xFF, 6 );
 #endif
 
 #if defined(MBEDTLS_DHM_C) && defined(MBEDTLS_SSL_SRV_C)