diff --git a/xo-interpreter2/include/xo/interpreter2/vsm/DVirtualSchematikaMachine.hpp b/xo-interpreter2/include/xo/interpreter2/vsm/DVirtualSchematikaMachine.hpp
index 84070673..e6badf83 100644
--- a/xo-interpreter2/include/xo/interpreter2/vsm/DVirtualSchematikaMachine.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/vsm/DVirtualSchematikaMachine.hpp
@@ -32,18 +32,33 @@ namespace xo {
             bool is_error() const;
 
             const obj<AGCObject> * value() const { return &result_; }
-            obj<AGCObject> & value_ref() { return result_; }
+            const obj<AGCObject> & value_ref() const { return result_; }
 
             /** result of evaluating first expression encountered in input **/
             obj<AGCObject> result_;
         };
 
-        /** vsm result + reamining span **/
-        struct VsmResultExt : public VsmResult {
+        /** vsm result + reamining span
+         *
+         *  Preserves address of wrapped VsmResult
+         *  (so it can continue to be owned by DVirtualSchematikaMachine,
+         *   and to be known to gc without add'l effort)
+         **/
+        struct VsmResultExt {
+            using AGCObject = xo::mm::AGCObject;
             using span_type = VsmResult::span_type;
 
             VsmResultExt() = default;
-            VsmResultExt(const VsmResult & result, span_type rem) : VsmResult{result}, remaining_{rem} {}
+            VsmResultExt(const VsmResult & result, span_type rem) : p_result_{&result}, remaining_{rem} {}
+
+            bool is_empty() const { return !p_result_; }
+            bool is_value() const { return p_result_ ? p_result_->is_value() : false; }
+            bool is_error() const { return p_result_ ? p_result_->is_error() : false; }
+
+            const obj<AGCObject> * value() const { return p_result_ ? p_result_->value() : nullptr; }
+            //const obj<AGCObject> & value_ref() { return result_.value_ref(); }
+
+            const VsmResult * p_result_ = nullptr;
 
             /** unconsumed portion of input **/
             VsmResult::span_type remaining_;
diff --git a/xo-interpreter2/src/interpreter2/DVirtualSchematikaMachine.cpp b/xo-interpreter2/src/interpreter2/DVirtualSchematikaMachine.cpp
index 9ceb8fac..f9977eb9 100644
--- a/xo-interpreter2/src/interpreter2/DVirtualSchematikaMachine.cpp
+++ b/xo-interpreter2/src/interpreter2/DVirtualSchematikaMachine.cpp
@@ -197,6 +197,8 @@ namespace xo {
 
                     auto error = obj<AGCObject,DRuntimeError>(DRuntimeError::_make(mm_.to_op(), src, msg));
 
+                    this->value_ = VsmResult(error);
+
                     {
                         obj<APrintable> error_pr
                             = FacetRegistry::instance().variant<APrintable,AGCObject>(error);
@@ -206,7 +208,7 @@ namespace xo {
                         pps.prettyn(error_pr);
                     }
 
-                    return VsmResultExt(VsmResult(error), remaining);
+                    return VsmResultExt(value_, remaining);
                 } else {
                     // incomplete input
                     return VsmResultExt(VsmResult(), remaining);
@@ -215,7 +217,7 @@ namespace xo {
 
             // here: have obtained complete input expression
 
-            VsmResult evalresult = this->start_eval(expr);
+            const VsmResult & evalresult = this->start_eval(expr);
 
             if (evalresult.is_error()) {
                 // TODO: print error here
@@ -239,7 +241,7 @@ namespace xo {
                 pps.prettyn(value_pr);
             }
 
-            return VsmResultExt(VsmResult(value), remaining);
+            return VsmResultExt(evalresult, remaining);
         }
 
         const VsmResult &
@@ -975,7 +977,7 @@ namespace xo {
             gc.forward_inplace(&fn_);
             gc.forward_inplace(&args_);
             if (value_.is_value()) {
-                gc.forward_inplace(&value_.value_ref());
+                gc.forward_inplace(const_cast<obj<AGCObject> *>(&value_.value_ref()));
             }
 
             return this->shallow_size();
diff --git a/xo-interpreter2/utest/VirtualSchematikaMachine.test.cpp b/xo-interpreter2/utest/VirtualSchematikaMachine.test.cpp
index ac74bab3..aabda3a3 100644
--- a/xo-interpreter2/utest/VirtualSchematikaMachine.test.cpp
+++ b/xo-interpreter2/utest/VirtualSchematikaMachine.test.cpp
@@ -103,6 +103,8 @@ namespace xo {
             {
                 scope log(XO_DEBUG(debug_flag));
 
+                // WARNING: res.value() is unstable - gc may move it
+
                 VsmResultExt res = vsm_->read_eval_print(input_span, eof_flag);
 
                 REQUIRE(res.is_value());