diff --git a/src/libsodium/crypto_secretbox/crypto_secretbox_easy.c b/src/libsodium/crypto_secretbox/crypto_secretbox_easy.c
index 12132a2a..5d58adc7 100644
--- a/src/libsodium/crypto_secretbox/crypto_secretbox_easy.c
+++ b/src/libsodium/crypto_secretbox/crypto_secretbox_easy.c
@@ -27,6 +27,13 @@ crypto_secretbox_detached(unsigned char *c, unsigned char *mac,
 
     crypto_core_hsalsa20(subkey, n, k, NULL);
 
+    /* Allow the m and and c buffer to partially overlap, by calling
+       memmove() if necessary.
+
+       Note that there is no fully portable way to compare pointers.
+       Some tools even report undefined behavior, despite the conversion.
+       Nevertheless, this works on all supported platforms.
+    */
     if (((uintptr_t) c > (uintptr_t) m &&
          (uintptr_t) c - (uintptr_t) m < mlen) ||
         ((uintptr_t) m > (uintptr_t) c &&
@@ -101,6 +108,13 @@ crypto_secretbox_open_detached(unsigned char *m, const unsigned char *c,
     if (m == NULL) {
         return 0;
     }
+    /* Allow the m and and c buffer to partially overlap, by calling
+       memmove() if necessary.
+
+       Note that there is no fully portable way to compare pointers.
+       Some tools even report undefined behavior, despite the conversion.
+       Nevertheless, this works on all supported platforms.
+    */
     if (((uintptr_t) c > (uintptr_t) m &&
          (uintptr_t) c - (uintptr_t) m < clen) ||
         ((uintptr_t) m > (uintptr_t) c &&
diff --git a/src/libsodium/crypto_secretbox/xchacha20poly1305/secretbox_xchacha20poly1305.c b/src/libsodium/crypto_secretbox/xchacha20poly1305/secretbox_xchacha20poly1305.c
index d012b13b..3459ee5b 100644
--- a/src/libsodium/crypto_secretbox/xchacha20poly1305/secretbox_xchacha20poly1305.c
+++ b/src/libsodium/crypto_secretbox/xchacha20poly1305/secretbox_xchacha20poly1305.c
@@ -31,6 +31,13 @@ crypto_secretbox_xchacha20poly1305_detached(unsigned char *c,
 
     crypto_core_hchacha20(subkey, n, k, NULL);
 
+    /* Allow the m and and c buffer to partially overlap, by calling
+       memmove() if necessary.
+
+       Note that there is no fully portable way to compare pointers.
+       Some tools even report undefined behavior, despite the conversion.
+       Nevertheless, this works on all supported platforms.
+    */
     if (((uintptr_t) c > (uintptr_t) m &&
          (uintptr_t) c - (uintptr_t) m < mlen) ||
         ((uintptr_t) m > (uintptr_t) c &&
@@ -108,6 +115,13 @@ crypto_secretbox_xchacha20poly1305_open_detached(unsigned char *m,
     if (m == NULL) {
         return 0;
     }
+    /* Allow the m and and c buffer to partially overlap, by calling
+       memmove() if necessary.
+
+       Note that there is no fully portable way to compare pointers.
+       Some tools even report undefined behavior, despite the conversion.
+       Nevertheless, this works on all supported platforms.
+    */
     if (((uintptr_t) c > (uintptr_t) m &&
          (uintptr_t) c - (uintptr_t) m < clen) ||
         ((uintptr_t) m > (uintptr_t) c &&