diff --git a/include/qom/object.h b/include/qom/object.h
index 13847fb..1a7b71a 100644
--- a/include/qom/object.h
+++ b/include/qom/object.h
@@ -586,13 +586,14 @@
 /**
  * object_initialize_with_type:
  * @data: A pointer to the memory to be used for the object.
+ * @size: The maximum size available at @data for the object.
  * @type: The type of the object to instantiate.
  *
  * This function will initialize an object.  The memory for the object should
  * have already been allocated.  The returned object has a reference count of 1,
  * and will be finalized when the last reference is dropped.
  */
-void object_initialize_with_type(void *data, Type type);
+void object_initialize_with_type(void *data, size_t size, Type type);
 
 /**
  * object_initialize:
diff --git a/qom/object.c b/qom/object.c
index 1635422..e90e382 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -311,7 +311,7 @@
     }
 }
 
-void object_initialize_with_type(void *data, TypeImpl *type)
+void object_initialize_with_type(void *data, size_t size, TypeImpl *type)
 {
     Object *obj = data;
 
@@ -320,6 +320,7 @@
 
     g_assert(type->instance_size >= sizeof(Object));
     g_assert(type->abstract == false);
+    g_assert(size >= type->instance_size);
 
     memset(obj, 0, type->instance_size);
     obj->class = type->class;
@@ -333,7 +334,7 @@
 {
     TypeImpl *type = type_get_by_name(typename);
 
-    object_initialize_with_type(data, type);
+    object_initialize_with_type(data, size, type);
 }
 
 static inline bool object_property_is_child(ObjectProperty *prop)
@@ -424,7 +425,7 @@
     type_initialize(type);
 
     obj = g_malloc(type->instance_size);
-    object_initialize_with_type(obj, type);
+    object_initialize_with_type(obj, type->instance_size, type);
     obj->free = g_free;
 
     return obj;