diff --git a/dist-build/emscripten-symbols.def b/dist-build/emscripten-symbols.def
index 8ac770c3..9558a886 100644
--- a/dist-build/emscripten-symbols.def
+++ b/dist-build/emscripten-symbols.def
@@ -487,6 +487,7 @@ _randombytes_set_implementation 0 0
 _randombytes_stir 1 1
 _randombytes_uniform 1 1
 _sodium_add 0 0
+_sodium_alloc_overhead 0 0
 _sodium_allocarray 0 0
 _sodium_bin2hex 1 1
 _sodium_compare 0 0
diff --git a/src/libsodium/include/sodium/utils.h b/src/libsodium/include/sodium/utils.h
index 0a7aadb4..4586cc2a 100644
--- a/src/libsodium/include/sodium/utils.h
+++ b/src/libsodium/include/sodium/utils.h
@@ -120,6 +120,9 @@ int sodium_mprotect_readonly(void *ptr);
 SODIUM_EXPORT
 int sodium_mprotect_readwrite(void *ptr);
 
+SODIUM_EXPORT
+size_t sodium_alloc_overhead(size_t size);
+
 /* -------- */
 
 int _sodium_alloc_init(void);
diff --git a/src/libsodium/sodium/utils.c b/src/libsodium/sodium/utils.c
index bff6e359..8ef2e630 100644
--- a/src/libsodium/sodium/utils.c
+++ b/src/libsodium/sodium/utils.c
@@ -702,3 +702,13 @@ sodium_mprotect_readwrite(void *ptr)
 {
     return _sodium_mprotect(ptr, _mprotect_readwrite);
 }
+
+size_t
+sodium_alloc_overhead(size_t size)
+{
+#ifndef HAVE_ALIGNED_MALLOC
+    return unprotected_size == (size_t) 0U;
+#else
+    return _page_round((sizeof canary) + size) + page_size * (size_t) 3U;
+#endif
+}
diff --git a/test/default/sodium_utils3.c b/test/default/sodium_utils3.c
index 3f2b600e..4bd7eb5a 100644
--- a/test/default/sodium_utils3.c
+++ b/test/default/sodium_utils3.c
@@ -37,6 +37,9 @@ main(void)
     void * buf;
     size_t size;
 
+    assert(sodium_alloc_overhead((size_t) 0U) !=
+           sodium_alloc_overhead((size_t) 65537U));
+
 #ifdef SIGSEGV
     signal(SIGSEGV, segv_handler);
 #endif