diff --git a/src/lib/diff/tree-mutator-collection-binding.hpp b/src/lib/diff/tree-mutator-collection-binding.hpp
index f778ae48c..e90199089 100644
--- a/src/lib/diff/tree-mutator-collection-binding.hpp
+++ b/src/lib/diff/tree-mutator-collection-binding.hpp
@@ -128,6 +128,12 @@ namespace diff{
           , openSub(u)
           { }
         
+        // allow move construction only,
+        // to enable use of unique_ptr in collections
+        CollectionBinding(CollectionBinding&&) = default;
+        CollectionBinding(CollectionBinding&) = delete;
+        
+        
         
         /* === content manipulation API === */
         
@@ -259,9 +265,9 @@ namespace diff{
         
         
       public:
-        ChildCollectionMutator(BIN wiringClosures, PAR&& chain)
+        ChildCollectionMutator(BIN&& wiringClosures, PAR&& chain)
           : PAR(std::forward<PAR>(chain))
-          , binding_(wiringClosures)
+          , binding_(forward<BIN>(wiringClosures))
           , pos_(binding_.initMutation())
           { }
         
@@ -280,7 +286,7 @@ namespace diff{
           {
             if (binding_.isApplicable(n))
               {
-                binding_.inject (binding_.construct(n));
+                binding_.inject (std::move (binding_.construct(n)));
                 return true;
               }
             else
diff --git a/src/lib/diff/tree-mutator.hpp b/src/lib/diff/tree-mutator.hpp
index 822a7bebf..5c74bae99 100644
--- a/src/lib/diff/tree-mutator.hpp
+++ b/src/lib/diff/tree-mutator.hpp
@@ -411,7 +411,8 @@ namespace diff{
          *   - the _matcher closure_ (CollectionBindingBuilder::matchElement) defines
          *     how to determine, if an implementation data element "matches" a given diff spec
          *   - the _constructor closure_ (CollectionBindingBuilder::constructFrom) defines how
-         *     to build a new implementation data element from the spec of an `INS` diff verb
+         *     to build a new implementation data element from the spec of an `INS` diff verb.
+         *     Note: the result will be moved (move-constructed) into the target container.
          *   - the optional _selector closure_ (CollectionBindingBuilder::isApplicableIf)
          *     allows to limit applicability of this whole binding (layer) to only some
          *     diff specs. E.g., we may set up a binding for elements with value semantics
diff --git a/tests/gui/test/mock-elm.hpp b/tests/gui/test/mock-elm.hpp
index 944354a09..19bbf2289 100644
--- a/tests/gui/test/mock-elm.hpp
+++ b/tests/gui/test/mock-elm.hpp
@@ -92,7 +92,7 @@ namespace test{
   using std::string;
   
   class MockElm;
-  using PMockElm = std::shared_ptr<MockElm>;
+  using PMockElm = std::unique_ptr<MockElm>;
   
   
   /**
@@ -252,7 +252,7 @@ namespace test{
                         })
                      .constructFrom ([&](GenNode const& spec) -> PMockElm
                         {
-                          return std::make_shared<MockElm>(spec.idi, this->uiBus_); // create a child element wired via this Element's BusTerm
+                          return std::make_unique<MockElm>(spec.idi, this->uiBus_); // create a child element wired via this Element's BusTerm
                         })
                      .buildChildMutator ([&](PMockElm& target, GenNode::ID const& subID, TreeMutator::Handle buff) -> bool
                         {