diff --git a/arch/platform/cc2538dk/contiki-conf.h b/arch/platform/cc2538dk/contiki-conf.h
index 307b015fe..a3ef81196 100644
--- a/arch/platform/cc2538dk/contiki-conf.h
+++ b/arch/platform/cc2538dk/contiki-conf.h
@@ -47,7 +47,14 @@ typedef uint32_t rtimer_clock_t;
 #define RADIO_DELAY_BEFORE_DETECT 0
 #ifndef TSCH_CONF_BASE_DRIFT_PPM
 /* The drift compared to "true" 10ms slots.
- * Enable adaptive sync to enable compensation for this. */
+ * Enable adaptive sync to enable compensation for this.
+ * Slot length 10000 usec
+ *             328 ticks
+ * Tick duration 30.517578125 usec
+ * Real slot duration 10009.765625 usec
+ * Target - real duration = -9.765625 usec
+ * TSCH_CONF_BASE_DRIFT_PPM -977
+ */
 #define TSCH_CONF_BASE_DRIFT_PPM -977
 #endif
 /*---------------------------------------------------------------------------*/
diff --git a/arch/platform/jn516x/platform-conf.h b/arch/platform/jn516x/platform-conf.h
index 703826ce7..3caadae2f 100644
--- a/arch/platform/jn516x/platform-conf.h
+++ b/arch/platform/jn516x/platform-conf.h
@@ -110,9 +110,15 @@ typedef uint32_t rtimer_clock_t;
 
 /* If the timer base a binary 32kHz clock, compensate for this base drift */
 #if RTIMER_USE_32KHZ && JN516X_EXTERNAL_CRYSTAL_OSCILLATOR
-/* Drift calculated using this formula:
-*    ((US_TO_TICKS(10000) * 100) - RTIMER_SECOND) * 1e6 = 976.5625 ppm
-*/
+/* The drift compared to "true" 10ms slots.
+ * Enable adaptive sync to enable compensation for this.
+ * Slot length 10000 usec
+ *             328 ticks
+ * Tick duration 30.517578125 usec
+ * Real slot duration 10009.765625 usec
+ * Target - real duration = -9.765625 usec
+ * TSCH_CONF_BASE_DRIFT_PPM -977
+ */
 #define TSCH_CONF_BASE_DRIFT_PPM -977
 #endif
 
diff --git a/arch/platform/openmote-cc2538/contiki-conf.h b/arch/platform/openmote-cc2538/contiki-conf.h
index d28a85ba3..5e7e967da 100644
--- a/arch/platform/openmote-cc2538/contiki-conf.h
+++ b/arch/platform/openmote-cc2538/contiki-conf.h
@@ -86,7 +86,14 @@ typedef uint32_t rtimer_clock_t;
 #define RADIO_DELAY_BEFORE_DETECT 0
 #ifndef TSCH_CONF_BASE_DRIFT_PPM
 /* The drift compared to "true" 10ms slots.
- * Enable adaptive sync to enable compensation for this. */
+ * Enable adaptive sync to enable compensation for this.
+ * Slot length 10000 usec
+ *             328 ticks
+ * Tick duration 30.517578125 usec
+ * Real slot duration 10009.765625 usec
+ * Target - real duration = -9.765625 usec
+ * TSCH_CONF_BASE_DRIFT_PPM -977
+ */
 #define TSCH_CONF_BASE_DRIFT_PPM -977
 #endif
 /*---------------------------------------------------------------------------*/
diff --git a/arch/platform/srf06-cc26xx/contiki-conf.h b/arch/platform/srf06-cc26xx/contiki-conf.h
index bb51131e9..4f464809a 100644
--- a/arch/platform/srf06-cc26xx/contiki-conf.h
+++ b/arch/platform/srf06-cc26xx/contiki-conf.h
@@ -280,7 +280,14 @@ typedef uint32_t rtimer_clock_t;
 
 #ifndef TSCH_CONF_BASE_DRIFT_PPM
 /* The drift compared to "true" 10ms slots.
- * Enable adaptive sync to enable compensation for this. */
+ * Enable adaptive sync to enable compensation for this.
+ * Slot length 10000 usec
+ *             328 ticks
+ * Tick duration 30.517578125 usec
+ * Real slot duration 10009.765625 usec
+ * Target - real duration = -9.765625 usec
+ * TSCH_CONF_BASE_DRIFT_PPM -977
+ */
 #define TSCH_CONF_BASE_DRIFT_PPM -977
 #endif
 
diff --git a/arch/platform/zoul/contiki-conf.h b/arch/platform/zoul/contiki-conf.h
index 38b34e5ad..a67e37e2c 100644
--- a/arch/platform/zoul/contiki-conf.h
+++ b/arch/platform/zoul/contiki-conf.h
@@ -84,7 +84,14 @@ typedef uint32_t rtimer_clock_t;
 #define RADIO_DELAY_BEFORE_DETECT 0
 #ifndef TSCH_CONF_BASE_DRIFT_PPM
 /* The drift compared to "true" 10ms slots.
- * Enable adaptive sync to enable compensation for this. */
+ * Enable adaptive sync to enable compensation for this.
+ * Slot length 10000 usec
+ *             328 ticks
+ * Tick duration 30.517578125 usec
+ * Real slot duration 10009.765625 usec
+ * Target - real duration = -9.765625 usec
+ * TSCH_CONF_BASE_DRIFT_PPM -977
+ */
 #define TSCH_CONF_BASE_DRIFT_PPM -977
 #endif
 /*---------------------------------------------------------------------------*/
diff --git a/os/net/mac/tsch/tsch-adaptive-timesync.c b/os/net/mac/tsch/tsch-adaptive-timesync.c
index 430db841d..5d9774537 100644
--- a/os/net/mac/tsch/tsch-adaptive-timesync.c
+++ b/os/net/mac/tsch/tsch-adaptive-timesync.c
@@ -68,7 +68,7 @@ tsch_adaptive_timesync_get_drift_ppm(void)
 /*---------------------------------------------------------------------------*/
 /* Add a value to a moving average estimator */
 static int32_t
-timesync_entry_add(int32_t val, uint32_t time_delta)
+timesync_entry_add(int32_t val)
 {
 #define NUM_TIMESYNC_ENTRIES 8
   static int32_t buffer[NUM_TIMESYNC_ENTRIES];
@@ -101,9 +101,9 @@ timesync_learn_drift_ticks(uint32_t time_delta_asn, int32_t drift_ticks)
   /* should fit in a 32-bit integer */
   int32_t time_delta_ticks = time_delta_asn * tsch_timing[tsch_ts_timeslot_length];
   int32_t real_drift_ticks = drift_ticks + compensated_ticks;
-  int32_t last_drift_ppm = (int32_t)((int64_t)real_drift_ticks * TSCH_DRIFT_UNIT / time_delta_ticks);
+  int32_t last_drift_ppm = (int32_t)(((int64_t)real_drift_ticks * TSCH_DRIFT_UNIT) / time_delta_ticks);
 
-  drift_ppm = timesync_entry_add(last_drift_ppm, time_delta_ticks);
+  drift_ppm = timesync_entry_add(last_drift_ppm);
 
   TSCH_LOG_ADD(tsch_log_message,
       snprintf(log->message, sizeof(log->message),
diff --git a/os/net/mac/tsch/tsch-security.c b/os/net/mac/tsch/tsch-security.c
index d0a5f85e5..b132e5882 100644
--- a/os/net/mac/tsch/tsch-security.c
+++ b/os/net/mac/tsch/tsch-security.c
@@ -138,6 +138,7 @@ tsch_security_secure_frame(uint8_t *hdr, uint8_t *outbuf,
   uint8_t with_encryption;
   uint8_t mic_len;
   uint8_t nonce[16];
+  struct ieee802154_ies ies;
 
   uint8_t a_len;
   uint8_t m_len;
@@ -151,6 +152,13 @@ tsch_security_secure_frame(uint8_t *hdr, uint8_t *outbuf,
     return 0;
   }
 
+  memset(&ies, 0, sizeof(ies));
+  if(frame802154e_parse_information_elements(hdr + hdrlen, datalen, &ies) > 0) {
+    /* put Header IEs into the header part which is not encrypted */
+    hdrlen += ies.ie_payload_ie_offset;
+    datalen -= ies.ie_payload_ie_offset;
+  }
+
   if(!frame.fcf.security_enabled) {
     /* Security is not enabled for this frame, we're done */
     return 0;
@@ -204,6 +212,7 @@ tsch_security_parse_frame(const uint8_t *hdr, int hdrlen, int datalen,
   uint8_t nonce[16];
   uint8_t a_len;
   uint8_t m_len;
+  struct ieee802154_ies ies;
 
   if(frame == NULL || hdr == NULL || hdrlen < 0 || datalen < 0) {
     return 0;
@@ -229,6 +238,12 @@ tsch_security_parse_frame(const uint8_t *hdr, int hdrlen, int datalen,
     return 0;
   }
 
+  memset(&ies, 0, sizeof(ies));
+  (void)frame802154e_parse_information_elements(hdr + hdrlen, datalen, &ies);
+  /* put Header IEs into the header part which is not encrypted */
+  hdrlen += ies.ie_payload_ie_offset;
+  datalen -= ies.ie_payload_ie_offset;
+
   tsch_security_init_nonce(nonce, sender, asn);
 
   if(with_encryption) {
diff --git a/os/net/mac/tsch/tsch-slot-operation.c b/os/net/mac/tsch/tsch-slot-operation.c
index d84a1998d..715b9463d 100644
--- a/os/net/mac/tsch/tsch-slot-operation.c
+++ b/os/net/mac/tsch/tsch-slot-operation.c
@@ -763,6 +763,12 @@ PT_THREAD(tsch_rx_slot(struct pt *pt, struct rtimer *t))
 
         packet_duration = TSCH_PACKET_DURATION(current_input->len);
 
+        if(!frame_valid) {
+          TSCH_LOG_ADD(tsch_log_message,
+              snprintf(log->message, sizeof(log->message),
+              "!failed to parse frame %u %u", header_len, current_input->len));
+        }
+
         if(frame_valid) {
           if(frame.fcf.frame_type != FRAME802154_DATAFRAME
             && frame.fcf.frame_type != FRAME802154_BEACONFRAME) {
@@ -786,11 +792,6 @@ PT_THREAD(tsch_rx_slot(struct pt *pt, struct rtimer *t))
                 "!failed to authenticate frame %u", current_input->len));
             frame_valid = 0;
           }
-        } else {
-          TSCH_LOG_ADD(tsch_log_message,
-              snprintf(log->message, sizeof(log->message),
-              "!failed to parse frame %u %u", header_len, current_input->len));
-          frame_valid = 0;
         }
 #endif /* LLSEC802154_ENABLED */