diff --git a/packages/builtin/array.pony b/packages/builtin/array.pony
index a8961525d3..e36fce85d9 100644
--- a/packages/builtin/array.pony
+++ b/packages/builtin/array.pony
@@ -276,11 +276,12 @@ class Array[A] is Seq[A]
 
     error
 
-  fun clone(): Array[this->A!]^ =>
+  fun clone(): Array[this->A!] iso^ =>
     """
     Clone the array.
     """
-    let out = Array[this->A!](_size)
+    let size' = _size
+    let out = recover iso Array[this->A!](size') end
     _ptr._copy_to(out._ptr, _size)
     out
 
diff --git a/packages/collections/list.pony b/packages/collections/list.pony
index 948a5caef3..3a17bc1be9 100644
--- a/packages/collections/list.pony
+++ b/packages/collections/list.pony
@@ -190,11 +190,11 @@ class List[A] is Seq[A]
 
     this
 
-  fun clone(): List[this->A!]^ =>
+  fun clone(): List[this->A!] iso^ =>
     """
     Clone the list.
     """
-    let out = List[this->A!]
+    let out = recover iso List[this->A!] end
 
     for v in values() do
       out.push(v)
diff --git a/packages/collections/map.pony b/packages/collections/map.pony
index d4a649d285..03870a3e12 100644
--- a/packages/collections/map.pony
+++ b/packages/collections/map.pony
@@ -175,13 +175,14 @@ class HashMap[K, V, H: HashFunction[K] val]
     this
 
   fun clone[H2: HashFunction[this->K!] val = H]():
-    HashMap[this->K!, this->V!, H2]^
+    HashMap[this->K!, this->V!, H2] iso^
   =>
     """
     Create a clone. The key and value types may be different due to aliasing
     and viewpoint adaptation.
     """
-    let r = HashMap[this->K!, this->V!, H2](_size)
+    let size' = _size
+    let r = recover iso HashMap[this->K!, this->V!, H2](size') end
 
     for (k, v) in pairs() do
       r(k) = v
diff --git a/packages/collections/set.pony b/packages/collections/set.pony
index a291759dc4..861541275b 100644
--- a/packages/collections/set.pony
+++ b/packages/collections/set.pony
@@ -215,12 +215,13 @@ class HashSet[A, H: HashFunction[A!] val] is Ordered[HashSet[A, H] box]
     end
     r
 
-  fun clone[K: HashFunction[this->A!] val = H](): HashSet[this->A!, K]^ =>
+  fun clone[K: HashFunction[this->A!] val = H](): HashSet[this->A!, K] iso^ =>
     """
     Create a clone. The element type may be different due to aliasing and
     viewpoint adaptation.
     """
-    let r = HashSet[this->A!, K](size())
+    let size' = size()
+    let r = recover HashSet[this->A!, K](size') end
 
     for value in values() do
       r.set(value)