diff --git a/msgpack.c b/msgpack.c
index a3faf30..5226055 100644
--- a/msgpack.c
+++ b/msgpack.c
@@ -92,6 +92,7 @@ static void msgpack_init_globals(zend_msgpack_globals *msgpack_globals) /* {{{ *
     msgpack_globals->illegal_key_insert = 0;
     msgpack_globals->use_str8_serialization = 1;
     msgpack_globals->serialize.var_hash = NULL;
+    msgpack_globals->serialize.var_keep = NULL;
     msgpack_globals->serialize.level = 0;
 }
 /* }}} */
diff --git a/msgpack_pack.c b/msgpack_pack.c
index 85d2cd4..08ae989 100644
--- a/msgpack_pack.c
+++ b/msgpack_pack.c
@@ -55,11 +55,11 @@ static inline int msgpack_var_add(HashTable *var_hash, zval *var, zend_long *var
         var_noref = var;
     }
 
-    if ((Z_TYPE_P(var_noref) == IS_OBJECT) && Z_OBJCE_P(var_noref)) {
-        p = zend_print_long_to_buf(
-                id + sizeof(id) - 1,
-                (((size_t)Z_OBJCE_P(var_noref) << 5)
-                 | ((size_t)Z_OBJCE_P(var_noref) >> (sizeof(long) * 8 - 5))) + (long)Z_OBJ_HANDLE_P(var_noref));
+    if (Z_TYPE_P(var_noref) == IS_OBJECT) {
+        /* key objects by their zend_object address; the 'o' prefix keeps
+         * them apart from the (purely numeric) array keys */
+        p = zend_print_ulong_to_buf(id + sizeof(id) - 1, (zend_ulong)(zend_uintptr_t)Z_OBJ_P(var_noref));
+        *--p = 'o';
         len = id + sizeof(id) - 1 - p;
     } else if (Z_TYPE_P(var_noref) == IS_ARRAY) {
         p = zend_print_long_to_buf(id + sizeof(id) - 1, (long)(var_noref));
@@ -81,6 +81,14 @@ static inline int msgpack_var_add(HashTable *var_hash, zval *var, zend_long *var
     ZVAL_LONG(&zv, zend_hash_num_elements(var_hash) + 1);
     zend_hash_str_add(var_hash, p, len, &zv);
 
+    if (Z_TYPE_P(var_noref) == IS_OBJECT) {
+        /* keep the object alive until packing ends, so that its address
+         * cannot be reused by another (temporary) object */
+        ZVAL_OBJ(&zv, Z_OBJ_P(var_noref));
+        Z_ADDREF(zv);
+        zend_hash_next_index_insert(MSGPACK_G(serialize).var_keep, &zv);
+    }
+
     return 1;
 }
 /* }}} */
@@ -94,6 +102,8 @@ void msgpack_serialize_var_init(msgpack_serialize_data_t *var_hash) /* {{{ */ {
         ALLOC_HASHTABLE(*var_hash_ptr);
         zend_hash_init(*var_hash_ptr, 10, NULL, NULL, 0);
         MSGPACK_G(serialize).var_hash = *var_hash_ptr;
+        ALLOC_HASHTABLE(MSGPACK_G(serialize).var_keep);
+        zend_hash_init(MSGPACK_G(serialize).var_keep, 10, NULL, ZVAL_PTR_DTOR, 0);
     }
     ++MSGPACK_G(serialize).level;
 }
@@ -106,6 +116,9 @@ void msgpack_serialize_var_destroy(msgpack_serialize_data_t *var_hash) /* {{{ */
     if (!MSGPACK_G(serialize).level) {
         zend_hash_destroy(*var_hash_ptr);
         FREE_HASHTABLE(*var_hash_ptr);
+        zend_hash_destroy(MSGPACK_G(serialize).var_keep);
+        FREE_HASHTABLE(MSGPACK_G(serialize).var_keep);
+        MSGPACK_G(serialize).var_keep = NULL;
     }
 }
 /* }}} */
diff --git a/php_msgpack.h b/php_msgpack.h
index 0f4f610..85fb825 100644
--- a/php_msgpack.h
+++ b/php_msgpack.h
@@ -29,6 +29,7 @@ ZEND_BEGIN_MODULE_GLOBALS(msgpack)
 	zend_bool force_f32;
     struct {
         void *var_hash;
+        void *var_keep;
         unsigned level;
     } serialize;
 ZEND_END_MODULE_GLOBALS(msgpack)
diff --git a/tests/var_hash_collision.phpt b/tests/var_hash_collision.phpt
new file mode 100644
index 0000000..271170d
--- /dev/null
+++ b/tests/var_hash_collision.phpt
@@ -0,0 +1,62 @@
+--TEST--
+Object reference keys must not collide between objects of different classes
+--SKIPIF--
+<?php
+if (!extension_loaded("msgpack")) {
+    exit('skip because msgpack extension is missing');
+}
+?>
+--INI--
+memory_limit=1G
+--FILE--
+<?php
+class Item {
+    public $status;
+}
+
+class Status {
+}
+
+$status = new Status();
+$items = array();
+for ($i = 0; $i < 200000; $i++) {
+    $item = new Item();
+    $item->status = $status;
+    $items[] = $item;
+}
+
+$unpacked = msgpack_unpack(msgpack_pack($items));
+foreach ($unpacked as $idx => $value) {
+    if (!$value instanceof Item) {
+        echo "index $idx: expected Item, got " . get_class($value) . "\n";
+    }
+}
+
+// temporary objects created during packing must not be confused with later ones
+
+class Tmp {
+    public $v;
+    public function __construct($v) { $this->v = $v; }
+    public function __serialize(): array { return array(new Tmp2($this->v)); }
+    public function __unserialize(array $data): void { $this->v = $data[0]->v; }
+}
+
+class Tmp2 {
+    public $v;
+    public function __construct($v) { $this->v = $v; }
+}
+
+$list = array();
+for ($i = 0; $i < 100; $i++) {
+    $list[] = new Tmp($i);
+}
+$unpacked = msgpack_unpack(msgpack_pack($list));
+foreach ($unpacked as $idx => $value) {
+    if (!$value instanceof Tmp || $value->v !== $idx) {
+        echo "index $idx: wrong value\n";
+    }
+}
+echo "done\n";
+?>
+--EXPECT--
+done