diff --git a/core/net/mac/tsch/tsch-security.c b/core/net/mac/tsch/tsch-security.c
index 340155cfe..59abaf2cf 100644
--- a/core/net/mac/tsch/tsch-security.c
+++ b/core/net/mac/tsch/tsch-security.c
@@ -125,7 +125,7 @@ tsch_security_check_level(const frame802154_t *frame)
           frame->aux_hdr.key_index == required_key_index);
 }
 /*---------------------------------------------------------------------------*/
-int
+unsigned int
 tsch_security_mic_len(const frame802154_t *frame)
 {
   if(frame != NULL && frame->fcf.security_enabled) {
@@ -135,7 +135,7 @@ tsch_security_mic_len(const frame802154_t *frame)
   }
 }
 /*---------------------------------------------------------------------------*/
-int
+unsigned int
 tsch_security_secure_frame(uint8_t *hdr, uint8_t *outbuf,
                            int hdrlen, int datalen, struct asn_t *asn)
 {
@@ -198,7 +198,7 @@ tsch_security_secure_frame(uint8_t *hdr, uint8_t *outbuf,
   return mic_len;
 }
 /*---------------------------------------------------------------------------*/
-int
+unsigned int
 tsch_security_parse_frame(const uint8_t *hdr, int hdrlen, int datalen,
                           const frame802154_t *frame, const linkaddr_t *sender, struct asn_t *asn)
 {
diff --git a/core/net/mac/tsch/tsch-security.h b/core/net/mac/tsch/tsch-security.h
index 294b03c51..3d6e9bf78 100644
--- a/core/net/mac/tsch/tsch-security.h
+++ b/core/net/mac/tsch/tsch-security.h
@@ -122,22 +122,24 @@ typedef uint8_t aes_key[16];
  * \brief Return MIC length
  * \return The length of MIC (>= 0)
  */
-int tsch_security_mic_len(const frame802154_t *frame);
+unsigned int tsch_security_mic_len(const frame802154_t *frame);
 
 /**
  * \brief Protect a frame with encryption and/or MIC
  * \return The length of a generated MIC (>= 0)
  */
-int tsch_security_secure_frame(uint8_t *hdr, uint8_t *outbuf,
-                               int hdrlen, int datalen, struct asn_t *asn);
+unsigned int tsch_security_secure_frame(uint8_t *hdr, uint8_t *outbuf,
+                                        int hdrlen, int datalen,
+                                        struct asn_t *asn);
 
 /**
  * \brief Parse and check a frame protected with encryption and/or MIC
  * \retval 0 On error or security check failure (insecure frame)
  * \retval 1 On success or no need for security check (good frame)
  */
-int tsch_security_parse_frame(const uint8_t *hdr, int hdrlen, int datalen,
-                              const frame802154_t *frame,
-                              const linkaddr_t *sender, struct asn_t *asn);
+unsigned int tsch_security_parse_frame(const uint8_t *hdr, int hdrlen,
+                                       int datalen, const frame802154_t *frame,
+                                       const linkaddr_t *sender,
+                                       struct asn_t *asn);
 
 #endif /* __TSCH_SECURITY_H__ */