--- vendor/ocaml-lmdb/mdb.c	2026-02-11 11:32:57.000000000 +0800
+++ vendor/ocaml-lmdb/mdb.c	2026-03-06 07:33:19.000000000 +0800
@@ -35,6 +35,11 @@
 #ifndef _GNU_SOURCE
 #define _GNU_SOURCE 1
 #endif
+
+#ifdef __APPLE__
+#include <AvailabilityMacros.h>
+#endif
+
 #if defined(MDB_VL32) || defined(__WIN64__)
 #define _FILE_OFFSET_BITS	64
 #endif
@@ -243,6 +248,16 @@
 #define MISALIGNED_OK	1
 #endif
 
+#if defined(__APPLE__) && MAC_OS_X_VERSION_MIN_REQUIRED < 1060
+static int posix_memalign_fallback(void **memptr, size_t alignment, size_t size) {
+    void *ptr = malloc(size + alignment - 1);
+    if (!ptr) return ENOMEM;
+    *memptr = (void *)(((size_t)ptr + alignment - 1) & ~(alignment - 1));
+    return 0;
+}
+#define posix_memalign posix_memalign_fallback
+#endif
+
 #include "lmdb.h"
 #include "midl.h"