diff --git a/src/mme/mme-kdf.c b/src/mme/mme-kdf.c
index 32bd2fe86..b9df458e3 100644
--- a/src/mme/mme-kdf.c
+++ b/src/mme/mme-kdf.c
@@ -20,7 +20,7 @@
 #include "ogs-crypt.h"
 
 void mme_kdf_nas(uint8_t algorithm_type_distinguishers,
-    uint8_t algorithm_identity, uint8_t *kasme, uint8_t *knas)
+    uint8_t algorithm_identity, const uint8_t *kasme, uint8_t *knas)
 {
     uint8_t s[7];
     uint8_t out[32];
@@ -39,7 +39,7 @@ void mme_kdf_nas(uint8_t algorithm_type_distinguishers,
     memcpy(knas, out+16, 16);
 }
 
-void mme_kdf_enb(uint8_t *kasme, uint32_t ul_count, uint8_t *kenb)
+void mme_kdf_enb(const uint8_t *kasme, uint32_t ul_count, uint8_t *kenb)
 {
     uint8_t s[7];
 
@@ -54,7 +54,7 @@ void mme_kdf_enb(uint8_t *kasme, uint32_t ul_count, uint8_t *kenb)
     ogs_hmac_sha256(kasme, 32, s, 7, kenb, 32);
 }
 
-void mme_kdf_nh(uint8_t *kasme, uint8_t *sync_input, uint8_t *kenb)
+void mme_kdf_nh(const uint8_t *kasme, const uint8_t *sync_input, uint8_t *kenb)
 {
     uint8_t s[35];
 
diff --git a/src/mme/mme-kdf.h b/src/mme/mme-kdf.h
index b7c0060a1..61bd792d8 100644
--- a/src/mme/mme-kdf.h
+++ b/src/mme/mme-kdf.h
@@ -34,10 +34,10 @@
 */
 
 void mme_kdf_nas(uint8_t algorithm_type_distinguishers,
-    uint8_t algorithm_identity, uint8_t *kasme, uint8_t *knas);
+    uint8_t algorithm_identity, const uint8_t *kasme, uint8_t *knas);
 
-void mme_kdf_enb(uint8_t *kasme, uint32_t ul_count, uint8_t *kenb);
+void mme_kdf_enb(const uint8_t *kasme, uint32_t ul_count, uint8_t *kenb);
 
-void mme_kdf_nh(uint8_t *kasme, uint8_t *sync_input, uint8_t *kenb);
+void mme_kdf_nh(const uint8_t *kasme, const uint8_t *sync_input, uint8_t *kenb);
 
 #endif /* MME_KDF_H */