diff --git a/src/libsodium/crypto_secretbox/crypto_secretbox.c b/src/libsodium/crypto_secretbox/crypto_secretbox.c
index 06801ee1..456f9f0a 100644
--- a/src/libsodium/crypto_secretbox/crypto_secretbox.c
+++ b/src/libsodium/crypto_secretbox/crypto_secretbox.c
@@ -25,6 +25,12 @@ crypto_secretbox_boxzerobytes(void)
     return crypto_secretbox_BOXZEROBYTES;
 }
 
+size_t
+crypto_secretbox_macbytes(void)
+{
+    return crypto_secretbox_MACBYTES;
+}
+
 const char *
 crypto_secretbox_primitive(void)
 {
diff --git a/src/libsodium/crypto_secretbox/xsalsa20poly1305/secretbox_xsalsa20poly1305_api.c b/src/libsodium/crypto_secretbox/xsalsa20poly1305/secretbox_xsalsa20poly1305_api.c
index 498437f3..21786924 100644
--- a/src/libsodium/crypto_secretbox/xsalsa20poly1305/secretbox_xsalsa20poly1305_api.c
+++ b/src/libsodium/crypto_secretbox/xsalsa20poly1305/secretbox_xsalsa20poly1305_api.c
@@ -20,6 +20,11 @@ crypto_secretbox_xsalsa20poly1305_boxzerobytes(void) {
     return crypto_secretbox_xsalsa20poly1305_BOXZEROBYTES;
 }
 
+size_t
+crypto_secretbox_xsalsa20poly1305_macbytes(void) {
+    return crypto_secretbox_xsalsa20poly1305_MACBYTES;
+}
+
 const char *
 crypto_secretbox_xsalsa20poly1305_primitive(void) {
     return "xsalsa20poly1305";
diff --git a/src/libsodium/include/sodium/crypto_secretbox.h b/src/libsodium/include/sodium/crypto_secretbox.h
index eb14bc52..3d064e5d 100644
--- a/src/libsodium/include/sodium/crypto_secretbox.h
+++ b/src/libsodium/include/sodium/crypto_secretbox.h
@@ -26,6 +26,10 @@ size_t  crypto_secretbox_zerobytes(void);
 SODIUM_EXPORT
 size_t  crypto_secretbox_boxzerobytes(void);
 
+#define crypto_secretbox_MACBYTES crypto_secretbox_xsalsa20poly1305_MACBYTES
+SODIUM_EXPORT
+size_t  crypto_secretbox_macbytes(void);
+
 #define crypto_secretbox_PRIMITIVE "xsalsa20poly1305"
 SODIUM_EXPORT
 const char *crypto_secretbox_primitive(void);
diff --git a/src/libsodium/include/sodium/crypto_secretbox_xsalsa20poly1305.h b/src/libsodium/include/sodium/crypto_secretbox_xsalsa20poly1305.h
index 22f0d667..0b006879 100644
--- a/src/libsodium/include/sodium/crypto_secretbox_xsalsa20poly1305.h
+++ b/src/libsodium/include/sodium/crypto_secretbox_xsalsa20poly1305.h
@@ -8,6 +8,7 @@
 #define crypto_secretbox_xsalsa20poly1305_NONCEBYTES 24U
 #define crypto_secretbox_xsalsa20poly1305_ZEROBYTES 32U
 #define crypto_secretbox_xsalsa20poly1305_BOXZEROBYTES 16U
+#define crypto_secretbox_xsalsa20poly1305_MACBYTES (crypto_secretbox_xsalsa20poly1305_ZEROBYTES - crypto_secretbox_xsalsa20poly1305_BOXZEROBYTES)
 
 #ifdef __cplusplus
 extern "C" {
@@ -25,6 +26,9 @@ size_t crypto_secretbox_xsalsa20poly1305_zerobytes(void);
 SODIUM_EXPORT
 size_t crypto_secretbox_xsalsa20poly1305_boxzerobytes(void);
 
+SODIUM_EXPORT
+size_t crypto_secretbox_xsalsa20poly1305_macbytes(void);
+
 SODIUM_EXPORT
 const char * crypto_secretbox_xsalsa20poly1305_primitive(void);