diff --git a/xo-alloc/include/xo/alloc/Forwarding1.hpp b/xo-alloc/include/xo/alloc/Forwarding1.hpp
index 6276c1ad..77e081f9 100644
--- a/xo-alloc/include/xo/alloc/Forwarding1.hpp
+++ b/xo-alloc/include/xo/alloc/Forwarding1.hpp
@@ -30,7 +30,7 @@ namespace xo {
             /** required by Object i/face, but never called on Forwarding1 **/
             virtual std::size_t _shallow_size() const final override;
             /** required by Object i/face, but never called on Forwarding1 **/
-            virtual Object *    _shallow_copy() const final override;
+            virtual Object *    _shallow_copy(gc::IAlloc * mm) const final override;
             /** required by Object i/face, but never called on Forwarding1 **/
             virtual std::size_t _forward_children() final override;
 
diff --git a/xo-alloc/include/xo/alloc/Object.hpp b/xo-alloc/include/xo/alloc/Object.hpp
index 5727331e..849cf9bb 100644
--- a/xo-alloc/include/xo/alloc/Object.hpp
+++ b/xo-alloc/include/xo/alloc/Object.hpp
@@ -57,6 +57,9 @@ namespace xo {
                 return (u2 <= u1 + sizeof(std::uintptr_t));
         }
 
+        /** (for consistency's sake) **/
+        T * get() const { return ptr_; }
+
         T * ptr() const { return ptr_; }
         T ** ptr_address() { return &ptr_; }
 
@@ -204,7 +207,7 @@ namespace xo {
          *
          *  Require: @ref mm is an instance of @ref gc::GC
          **/
-        virtual Object * _shallow_copy() const = 0;
+        virtual Object * _shallow_copy(gc::IAlloc * mm) const = 0;
 
         /** update child pointers that refer to forwarding pointers,
          *  replacing them with the correct destination.
diff --git a/xo-alloc/src/alloc/Forwarding1.cpp b/xo-alloc/src/alloc/Forwarding1.cpp
index 4b47e4f2..b4a44ff6 100644
--- a/xo-alloc/src/alloc/Forwarding1.cpp
+++ b/xo-alloc/src/alloc/Forwarding1.cpp
@@ -52,7 +52,7 @@ namespace xo {
 
         // LCOV_EXCL_START
         Object *
-        Forwarding1::_shallow_copy() const {
+        Forwarding1::_shallow_copy(gc::IAlloc *) const {
             assert(false);
             return nullptr;
         }
diff --git a/xo-alloc/src/alloc/Object.cpp b/xo-alloc/src/alloc/Object.cpp
index 475d84ad..309e0886 100644
--- a/xo-alloc/src/alloc/Object.cpp
+++ b/xo-alloc/src/alloc/Object.cpp
@@ -170,7 +170,7 @@ namespace xo {
          */
         if (gc->fromspace_contains(src))
         {
-            Object * dest = src->_shallow_copy();
+            Object * dest = src->_shallow_copy(gc);
 
             if (dest != src)
                 src->_forward_to(dest);
diff --git a/xo-interpreter/include/xo/interpreter/GlobalEnv.hpp b/xo-interpreter/include/xo/interpreter/GlobalEnv.hpp
index d45f9cb4..bed452da 100644
--- a/xo-interpreter/include/xo/interpreter/GlobalEnv.hpp
+++ b/xo-interpreter/include/xo/interpreter/GlobalEnv.hpp
@@ -12,6 +12,9 @@ namespace xo {
          *  @brief Top-level global environment
          **/
         class GlobalEnv : public Env {
+        public:
+            using map_type = std::map<std::string, gp<Object>>;
+
         public:
             /** Create top-level global environment, allocating via @p mm.
              *  Expect one of these per interpreter session.
@@ -19,7 +22,9 @@ namespace xo {
             static gp<GlobalEnv> make_empty(gc::IAlloc * mm,
                                             const rp<GlobalSymtab> & symtab);
 
+#ifdef NOT_USING
             gc::IAlloc * get_mm() const { return mm_; }
+#endif
 
             // inherited from Env..
             virtual bool local_contains_var(const std::string & vname) const final override;
@@ -29,10 +34,11 @@ namespace xo {
             virtual TaggedPtr self_tp() const final override;
             virtual void display(std::ostream & os) const final override;
             virtual std::size_t _shallow_size() const final override;
-            virtual Object * _shallow_copy() const final override;
+            virtual Object * _shallow_copy(gc::IAlloc * mm) const final override;
             virtual std::size_t _forward_children() final override;
 
         private:
+            GlobalEnv(const GlobalEnv & x);
             GlobalEnv(gc::IAlloc * mm, const rp<GlobalSymtab> & symtab);
 
         private:
@@ -56,7 +62,7 @@ namespace xo {
              *  TODO: probably want to hash here instead.
              *        May also want lhs names to be separately hashed symbols
              **/
-            std::map<std::string, gp<Object>> slot_map_;
+            up<map_type> slot_map_;
         };
     } /*namespace scm*/
 } /*namespace xo*/
diff --git a/xo-interpreter/include/xo/interpreter/LocalEnv.hpp b/xo-interpreter/include/xo/interpreter/LocalEnv.hpp
index f7515fa2..e762d7d7 100644
--- a/xo-interpreter/include/xo/interpreter/LocalEnv.hpp
+++ b/xo-interpreter/include/xo/interpreter/LocalEnv.hpp
@@ -102,7 +102,7 @@ namespace xo {
             virtual TaggedPtr self_tp() const final override;
             virtual void display(std::ostream & os) const final override;
             virtual std::size_t _shallow_size() const final override;
-            virtual Object * _shallow_copy() const final override;
+            virtual Object * _shallow_copy(gc::IAlloc * mm) const final override;
             virtual std::size_t _forward_children() final override;
 
         private:
diff --git a/xo-interpreter/src/interpreter/GlobalEnv.cpp b/xo-interpreter/src/interpreter/GlobalEnv.cpp
index 5ecb598d..38b9ff1c 100644
--- a/xo-interpreter/src/interpreter/GlobalEnv.cpp
+++ b/xo-interpreter/src/interpreter/GlobalEnv.cpp
@@ -16,9 +16,17 @@ namespace xo {
              return new GlobalEnv(mm, symtab);
         }
 
+        GlobalEnv::GlobalEnv(const GlobalEnv & x)
+            : mm_{x.mm_},
+              symtab_{x.symtab_},
+              slot_map_{std::make_unique<map_type>(*x.slot_map_)}
+        {
+        }
+
         GlobalEnv::GlobalEnv(gc::IAlloc * mm,
                              const rp<GlobalSymtab> & symtab) : mm_{mm},
-                                                                symtab_{symtab}
+                                                                symtab_{symtab},
+                                                                slot_map_{std::make_unique<map_type>()}
         {}
 
         bool
@@ -52,7 +60,7 @@ namespace xo {
 
             this->symtab_->require_global(var->name(), var);
 
-            this->slot_map_[var->name()] = gp<Object>();
+            (*this->slot_map_)[var->name()] = gp<Object>();
         }
 
         TaggedPtr
@@ -64,31 +72,29 @@ namespace xo {
         void
         GlobalEnv::display(std::ostream & os) const
         {
-            os << "<global-env" << xtag("n", slot_map_.size()) << ">";
+            os << "<global-env" << xtag("n", slot_map_->size()) << ">";
         }
 
         std::size_t
         GlobalEnv::_shallow_size() const
         {
-            /** 0: since not allocated in gc-space */
-            return 0;
+            return sizeof(GlobalEnv);
         }
 
         Object *
-        GlobalEnv::_shallow_copy() const
+        GlobalEnv::_shallow_copy(gc::IAlloc * mm) const
         {
-            /* by design, don't copy; not subject to GC */
-            return const_cast<GlobalEnv *>(this);
+            Cpof cpof(mm, this);
+
+            return new (cpof) GlobalEnv(*this);
         }
 
         std::size_t
         GlobalEnv::_forward_children()
         {
-            /* All global slots are treated as GC roots; this means we
-             * don't have to forward them
-             *
-             * This works only as long as global env is immortal.
-             */
+            for (auto & ix : *slot_map_) {
+                Object::_forward_inplace(ix.second);
+            }
             return _shallow_size();
         }
     } /*namespace scm*/
diff --git a/xo-interpreter/src/interpreter/LocalEnv.cpp b/xo-interpreter/src/interpreter/LocalEnv.cpp
index 38cea06d..6042d00d 100644
--- a/xo-interpreter/src/interpreter/LocalEnv.cpp
+++ b/xo-interpreter/src/interpreter/LocalEnv.cpp
@@ -97,9 +97,9 @@ namespace xo {
         }
 
         Object *
-        LocalEnv::_shallow_copy() const
+        LocalEnv::_shallow_copy(gc::IAlloc * mm) const
         {
-            Cpof cpof(Object::mm, this);
+            Cpof cpof(mm, this);
 
             size_t z = size();
 
diff --git a/xo-object/include/xo/object/Boolean.hpp b/xo-object/include/xo/object/Boolean.hpp
index 66f01ed7..e0b9217c 100644
--- a/xo-object/include/xo/object/Boolean.hpp
+++ b/xo-object/include/xo/object/Boolean.hpp
@@ -24,7 +24,7 @@ namespace xo {
             virtual TaggedPtr self_tp() const final override;
             virtual void display(std::ostream & os) const final override;
             virtual std::size_t _shallow_size() const final override;
-            virtual Object * _shallow_copy() const final override;
+            virtual Object * _shallow_copy(gc::IAlloc * mm) const final override;
             virtual std::size_t _forward_children() final override;
 
         private:
diff --git a/xo-object/include/xo/object/Float.hpp b/xo-object/include/xo/object/Float.hpp
index 7ca1a8c0..507aefff 100644
--- a/xo-object/include/xo/object/Float.hpp
+++ b/xo-object/include/xo/object/Float.hpp
@@ -29,7 +29,7 @@ namespace xo {
             virtual TaggedPtr self_tp() const final override;
             virtual void display(std::ostream & os) const final override;
             virtual std::size_t _shallow_size() const final override;
-            virtual Object * _shallow_copy() const final override;
+            virtual Object * _shallow_copy(gc::IAlloc * mm) const final override;
             virtual std::size_t _forward_children() final override;
 
         private:
diff --git a/xo-object/include/xo/object/Integer.hpp b/xo-object/include/xo/object/Integer.hpp
index 5f3a2d86..d3ebd22d 100644
--- a/xo-object/include/xo/object/Integer.hpp
+++ b/xo-object/include/xo/object/Integer.hpp
@@ -29,7 +29,7 @@ namespace xo {
             virtual TaggedPtr self_tp() const final override;
             virtual void display(std::ostream & os) const final override;
             virtual std::size_t _shallow_size() const final override;
-            virtual Object * _shallow_copy() const final override;
+            virtual Object * _shallow_copy(gc::IAlloc * mm) const final override;
             virtual std::size_t _forward_children() final override;
 
         private:
diff --git a/xo-object/include/xo/object/List.hpp b/xo-object/include/xo/object/List.hpp
index 6272d0a2..cc601a16 100644
--- a/xo-object/include/xo/object/List.hpp
+++ b/xo-object/include/xo/object/List.hpp
@@ -58,7 +58,7 @@ namespace xo {
             virtual TaggedPtr self_tp() const final override;
             virtual void display(std::ostream & os) const final override;
             virtual std::size_t _shallow_size() const final override;
-            virtual Object * _shallow_copy() const final override;
+            virtual Object * _shallow_copy(gc::IAlloc * mm) const final override;
             virtual std::size_t _forward_children() final override;
 
         private:
diff --git a/xo-object/include/xo/object/String.hpp b/xo-object/include/xo/object/String.hpp
index b63744aa..90d8c536 100644
--- a/xo-object/include/xo/object/String.hpp
+++ b/xo-object/include/xo/object/String.hpp
@@ -36,7 +36,7 @@ namespace xo {
             virtual TaggedPtr self_tp() const final override;
             virtual void display(std::ostream & os) const final override;
             virtual std::size_t _shallow_size() const final override;
-            virtual Object * _shallow_copy() const final override;
+            virtual Object * _shallow_copy(gc::IAlloc * mm) const final override;
             virtual std::size_t _forward_children() final override;
 
         private:
diff --git a/xo-object/src/object/Boolean.cpp b/xo-object/src/object/Boolean.cpp
index 43d822a3..13cf3f01 100644
--- a/xo-object/src/object/Boolean.cpp
+++ b/xo-object/src/object/Boolean.cpp
@@ -56,7 +56,7 @@ namespace xo {
 
         // LCOV_EXCL_START
         Object *
-        Boolean::_shallow_copy() const
+        Boolean::_shallow_copy(gc::IAlloc *) const
         {
 
             /* Boolean instances not created in GC-owned space,
diff --git a/xo-object/src/object/Float.cpp b/xo-object/src/object/Float.cpp
index b723dbfd..4939fa49 100644
--- a/xo-object/src/object/Float.cpp
+++ b/xo-object/src/object/Float.cpp
@@ -42,8 +42,8 @@ namespace xo {
         }
 
         Object *
-        Float::_shallow_copy() const {
-            Cpof cpof(Object::mm, this);
+        Float::_shallow_copy(gc::IAlloc * mm) const {
+            Cpof cpof(mm, this);
             return new (cpof) Float(*this);
         }
 
diff --git a/xo-object/src/object/Integer.cpp b/xo-object/src/object/Integer.cpp
index 4d5f663f..f5587b1f 100644
--- a/xo-object/src/object/Integer.cpp
+++ b/xo-object/src/object/Integer.cpp
@@ -43,8 +43,8 @@ namespace xo {
         }
 
         Object *
-        Integer::_shallow_copy() const {
-            Cpof cpof(Object::mm, this);
+        Integer::_shallow_copy(gc::IAlloc * mm) const {
+            Cpof cpof(mm, this);
             return new (cpof) Integer(*this);
         }
 
diff --git a/xo-object/src/object/List.cpp b/xo-object/src/object/List.cpp
index 91674920..a82c7cc5 100644
--- a/xo-object/src/object/List.cpp
+++ b/xo-object/src/object/List.cpp
@@ -97,12 +97,12 @@ namespace xo {
         }
 
         Object *
-        List::_shallow_copy() const {
-            scope log(XO_DEBUG(Object::mm->debug_flag()));
+        List::_shallow_copy(gc::IAlloc * mm) const {
+            scope log(XO_DEBUG(mm->debug_flag()));
 
             assert(!(this->is_nil()));
 
-            Cpof cpof(Object::mm, this);
+            Cpof cpof(mm, this);
 
             return new (cpof) List(*this);
         }
diff --git a/xo-object/src/object/String.cpp b/xo-object/src/object/String.cpp
index c5de286e..400d187c 100644
--- a/xo-object/src/object/String.cpp
+++ b/xo-object/src/object/String.cpp
@@ -126,11 +126,11 @@ namespace xo {
         }
 
         Object *
-        String::_shallow_copy() const
+        String::_shallow_copy(gc::IAlloc * mm) const
         {
             // Reminder: String must come before secondary allocation,
 
-            Cpof cpof(Object::mm, this);
+            Cpof cpof(mm, this);
 
             // might expect to write:
             //  gp<String> copy = new (gcm) String(Object::mm, owner_, z_chars_, chars_);