Index: src/OFObject.h
==================================================================
--- src/OFObject.h
+++ src/OFObject.h
@@ -351,10 +351,24 @@
  * @brief Returns whether the object is a proxy object.
  *
  * @return A boolean whether the object is a proxy object
  */
 - (bool)isProxy;
+
+/*!
+ * @brief Returns whether the class allows weak references.
+ *
+ * @return Whether the class allows weak references
+ */
+- (bool)allowsWeakReference;
+
+/*!
+ * @brief Retain a weak reference to this object.
+ *
+ * @return Whether a weak reference to this object has been retained
+ */
+- (bool)retainWeakReference;
 @end
 
 /*!
  * @class OFObject OFObject.h ObjFW/OFObject.h
  *

Index: src/runtime/arc.m
==================================================================
--- src/runtime/arc.m
+++ src/runtime/arc.m
@@ -154,11 +154,12 @@
 				break;
 			}
 		}
 	}
 
-	if (value != nil) {
+	if (value != nil && class_respondsToSelector(object_getClass(value),
+	    @selector(allowsWeakReference)) && [value allowsWeakReference]) {
 		struct weak_ref *ref = objc_hashtable_get(hashtable, value);
 
 		if (ref == NULL) {
 			if ((ref = calloc(1, sizeof(*ref))) == NULL)
 				OBJC_ERROR("Not enough memory to allocate weak "
@@ -171,11 +172,12 @@
 		    (ref->count + 1) * sizeof(id*))) == NULL)
 			OBJC_ERROR("Not enough memory to allocate weak "
 			    "reference!")
 
 		ref->locations[ref->count++] = object;
-	}
+	} else
+		value = nil;
 
 	*object = value;
 
 #ifdef OF_HAVE_THREADS
 	if (!of_spinlock_unlock(&spinlock))
@@ -186,27 +188,31 @@
 }
 
 id
 objc_loadWeakRetained(id *object)
 {
-	id ret = nil;
+	id value = nil;
 	struct weak_ref *ref;
 
 #ifdef OF_HAVE_THREADS
 	if (!of_spinlock_lock(&spinlock))
 		OBJC_ERROR("Failed to lock spinlock!")
 #endif
 
 	if ((ref = objc_hashtable_get(hashtable, *object)) != NULL)
-		ret = *object;
+		value = *object;
 
 #ifdef OF_HAVE_THREADS
 	if (!of_spinlock_unlock(&spinlock))
 		OBJC_ERROR("Failed to unlock spinlock!")
 #endif
 
-	return objc_retain(ret);
+	if (class_respondsToSelector(object_getClass(value),
+	    @selector(retainWeakReference)) && [value retainWeakReference])
+		return value;
+
+	return nil;
 }
 
 id
 objc_initWeak(id *object, id value)
 {