diff --git a/ChangeLog b/ChangeLog
index f1e5537d8676e4e4eccd91cc76d7e18708821542..fbef1af65d1d01bf11ba02966d3c5dbd1ccb032d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2022-12-05  Niels Möller  <nisse@lysator.liu.se>
+
+	* xts-aes128.c (xts_aes128_encrypt_message)
+	(xts_aes128_decrypt_message): const-declare the xts_key argument.
+	* xts-aes256.c (xts_aes256_encrypt_message)
+	(xts_aes256_decrypt_message): Likewise.
+
 2022-11-09  Niels Möller  <nisse@lysator.liu.se>
 
 	From Mamone Tarsha:
diff --git a/xts-aes128.c b/xts-aes128.c
index 5b447bb9586104392073c55699d79eb37f0e5bc7..2e04ad65538fcdd8f602660c815f5e522107fddc 100644
--- a/xts-aes128.c
+++ b/xts-aes128.c
@@ -56,7 +56,7 @@ xts_aes128_set_decrypt_key(struct xts_aes128_key *xts_key, const uint8_t *key)
 }
 
 void
-xts_aes128_encrypt_message(struct xts_aes128_key *xts_key,
+xts_aes128_encrypt_message(const struct xts_aes128_key *xts_key,
                            const uint8_t *tweak, size_t length,
                            uint8_t *dst, const uint8_t *src)
 {
@@ -66,7 +66,7 @@ xts_aes128_encrypt_message(struct xts_aes128_key *xts_key,
 }
 
 void
-xts_aes128_decrypt_message(struct xts_aes128_key *xts_key,
+xts_aes128_decrypt_message(const struct xts_aes128_key *xts_key,
                            const uint8_t *tweak, size_t length,
                            uint8_t *dst, const uint8_t *src)
 {
diff --git a/xts-aes256.c b/xts-aes256.c
index 2285b8c877473045c81b6c0aaacf92a3d9cc2669..65502d16e375d85b45297b3aeaec7d719ddae17d 100644
--- a/xts-aes256.c
+++ b/xts-aes256.c
@@ -56,7 +56,7 @@ xts_aes256_set_decrypt_key(struct xts_aes256_key *xts_key, const uint8_t *key)
 }
 
 void
-xts_aes256_encrypt_message(struct xts_aes256_key *xts_key,
+xts_aes256_encrypt_message(const struct xts_aes256_key *xts_key,
                            const uint8_t *tweak, size_t length,
                            uint8_t *dst, const uint8_t *src)
 {
@@ -66,7 +66,7 @@ xts_aes256_encrypt_message(struct xts_aes256_key *xts_key,
 }
 
 void
-xts_aes256_decrypt_message(struct xts_aes256_key *xts_key,
+xts_aes256_decrypt_message(const struct xts_aes256_key *xts_key,
                            const uint8_t *tweak, size_t length,
                            uint8_t *dst, const uint8_t *src)
 {
diff --git a/xts.h b/xts.h
index db906a2a49b308e0975c0e0dbc46aaaa0191b72a..904ba760b2464f942be829f63724c13012f3fb5c 100644
--- a/xts.h
+++ b/xts.h
@@ -83,12 +83,12 @@ xts_aes128_set_decrypt_key(struct xts_aes128_key *xts_key,
                            const uint8_t *key);
 
 void
-xts_aes128_encrypt_message(struct xts_aes128_key *xtskey,
+xts_aes128_encrypt_message(const struct xts_aes128_key *xtskey,
                            const uint8_t *tweak, size_t length,
                            uint8_t *dst, const uint8_t *src);
 
 void
-xts_aes128_decrypt_message(struct xts_aes128_key *xts_key,
+xts_aes128_decrypt_message(const struct xts_aes128_key *xts_key,
                            const uint8_t *tweak, size_t length,
                            uint8_t *dst, const uint8_t *src);
 
@@ -107,12 +107,12 @@ xts_aes256_set_decrypt_key(struct xts_aes256_key *xts_key,
                            const uint8_t *key);
 
 void
-xts_aes256_encrypt_message(struct xts_aes256_key *xts_key,
+xts_aes256_encrypt_message(const struct xts_aes256_key *xts_key,
                            const uint8_t *tweak, size_t length,
                            uint8_t *dst, const uint8_t *src);
 
 void
-xts_aes256_decrypt_message(struct xts_aes256_key *xts_key,
+xts_aes256_decrypt_message(const struct xts_aes256_key *xts_key,
                            const uint8_t *tweak, size_t length,
                            uint8_t *dst, const uint8_t *src);