diff --git a/nCompiler/inst/include/nCompiler/ET_Rcpp_ext/post_Rcpp/ETaccessor_post_Rcpp.h b/nCompiler/inst/include/nCompiler/ET_Rcpp_ext/post_Rcpp/ETaccessor_post_Rcpp.h
index 07dd3786..075b96a6 100644
--- a/nCompiler/inst/include/nCompiler/ET_Rcpp_ext/post_Rcpp/ETaccessor_post_Rcpp.h
+++ b/nCompiler/inst/include/nCompiler/ET_Rcpp_ext/post_Rcpp/ETaccessor_post_Rcpp.h
@@ -241,7 +241,7 @@ Scalar& ETaccessorBase::scalar() {
 // then specialize to allow valid types (Eigen::Tensor's or true scalars)
 // These are supported as run-time errors because the genericInterfaceC
 // will access them by a name.
-template<typename ERROR>
+template<typename ERROR, bool copy=false>
 class ETaccessor : public ETaccessorTyped<double> {
   public:
   using ET = Eigen::Tensor<double, 0>;
@@ -278,8 +278,8 @@ class ETaccessor : public ETaccessorTyped<double> {
 };
 
 
-template<typename Scalar, int nDim>
-class ETaccessor<Eigen::Tensor<Scalar, nDim> > : public ETaccessorTyped<Scalar> {
+template<typename Scalar, int nDim, bool copy>
+class ETaccessor<Eigen::Tensor<Scalar, nDim>, copy> : public ETaccessorTyped<Scalar> {
   public:
   using ET = Eigen::Tensor<Scalar, nDim>;
   // using Scalar = typename ET::Scalar;
@@ -306,7 +306,24 @@ class ETaccessor<Eigen::Tensor<Scalar, nDim> > : public ETaccessorTyped<Scalar>
   std::vector<int> intDims_;
 };
 
-template<typename Scalar>
+template<typename ET>
+struct ETaccessorCopyHolder {
+  ET obj_copy;
+  ETaccessorCopyHolder(const ET &src) : obj_copy(src) {}
+};
+
+template<typename Scalar, int nDim>
+class ETaccessor<Eigen::Tensor<Scalar, nDim>, true> : 
+  private ETaccessorCopyHolder<Eigen::Tensor<Scalar, nDim>>,
+  public ETaccessor<Eigen::Tensor<Scalar, nDim>, false> {
+public:
+  using ET = Eigen::Tensor<Scalar, nDim>;
+  using Holder = ETaccessorCopyHolder<ET>;
+  ETaccessor(const ET &obj_) : Holder(obj_), ETaccessor<ET, false>(Holder::obj_copy) {};
+  ~ETaccessor() {};
+};
+
+template<typename Scalar, bool copy=false>
 class ETaccessorScalar : public ETaccessorTyped<Scalar> {
   public:
   ETaccessorScalar(Scalar &obj_) : obj(obj_) {};
@@ -323,24 +340,38 @@ class ETaccessorScalar : public ETaccessorTyped<Scalar> {
   std::vector<int> intDims_;
 };
 
-template<>
-class ETaccessor<double> : public ETaccessorScalar<double> {
+template<typename Scalar>
+class ETaccessorScalar<Scalar, true> : 
+  private ETaccessorCopyHolder<Scalar>,
+  public ETaccessorScalar<Scalar, false> {
+public:
+  using ET = ETaccessorScalar<Scalar, false>;
+  using Holder = ETaccessorCopyHolder<Scalar>;
+  ETaccessorScalar(const Scalar &obj_) : Holder(obj_), ET(Holder::obj_copy) {};
+  ~ETaccessorScalar() {};
+};
+
+template<bool copy>
+class ETaccessor<double, copy> : public ETaccessorScalar<double, copy> {
+  using Ref = std::conditional_t<copy, const double&, double&>;
   public:
-  ETaccessor(double &obj_) : ETaccessorScalar(obj_) {};
+  ETaccessor(Ref obj_) : ETaccessorScalar<double, copy>(obj_) {};
   ~ETaccessor() {};
 };
 
-template<>
-class ETaccessor<int> : public ETaccessorScalar<int> {
+template<bool copy>
+class ETaccessor<int, copy> : public ETaccessorScalar<int, copy> {
+  using Ref = std::conditional_t<copy, const int&, int&>;
   public:
-  ETaccessor(int &obj_) : ETaccessorScalar(obj_) {};
+  ETaccessor(Ref obj_) : ETaccessorScalar<int, copy>(obj_) {};
   ~ETaccessor() {};
 };
 
-template<>
-class ETaccessor<bool> : public ETaccessorScalar<bool> {
+template<bool copy>
+class ETaccessor<bool, copy> : public ETaccessorScalar<bool, copy> {
+  using Ref = std::conditional_t<copy, const bool&, bool&>;
   public:
-  ETaccessor(bool &obj_) : ETaccessorScalar(obj_) {};
+  ETaccessor(Ref obj_) : ETaccessorScalar<bool, copy>(obj_) {};
   ~ETaccessor() {};
 };
 
@@ -351,9 +382,16 @@ Eigen::Tensor<Scalar, nDim> &ETaccessorBase::ref() {
   return castptr->innerRef();
 }
 
-template<typename T>
-auto ETaccess(T &x) -> ETaccessor<T>{
-  return ETaccessor<T>(x);
+template<bool copy=false, typename T>
+std::enable_if_t<!copy, ETaccessor<T, false>>
+ETaccess(T &x) {
+  return ETaccessor<T, false>(x);
+}
+
+template<bool copy, typename T>
+std::enable_if_t<copy, ETaccessor<T, true>>
+ETaccess(const T &x) {
+  return ETaccessor<T, true>(x);
 }
 
 // end ETaccess
diff --git a/nCompiler/inst/include/nCompiler/ET_Rcpp_ext/post_Rcpp/nC_as.h b/nCompiler/inst/include/nCompiler/ET_Rcpp_ext/post_Rcpp/nC_as.h
index c8001718..0b82774b 100644
--- a/nCompiler/inst/include/nCompiler/ET_Rcpp_ext/post_Rcpp/nC_as.h
+++ b/nCompiler/inst/include/nCompiler/ET_Rcpp_ext/post_Rcpp/nC_as.h
@@ -131,7 +131,7 @@ class CastingProxy {
 
 template<typename TargetType>
 class RuntimeCastingProxy {
-  // TargetType5o here should be a true scalar type,
+  // TargetType here should be a true scalar type,
   // because specialization to Eigen::Tensor types is below.
   typedef TargetType TargetScalar;
 
@@ -273,9 +273,9 @@ class RuntimeCastingProxy<Eigen::Tensor<TargetScalar, nDim> > {
 
 // Compile-time source: delegates to ETaccessorTyped<Scalar>::asTyped<>().
 // Returns EmptyProxy<TM>, EmptyProxy<STM>, RHSCastProxy, or CastingProxy.
-template<typename TargetType, AsMode mode = AsMode::TM, typename T>
+template<typename TargetType, AsMode mode = AsMode::TM, bool copy = false, typename T>
 auto as_nC(T& x) {
-  return ETaccess(x).template asTyped<TargetType, mode>();
+  return ETaccess<copy>(x).template asTyped<TargetType, mode>();
 }
 
 // Runtime source: scalar type of acc is unknown at compile time.
diff --git a/nCompiler/tests/testthat/cpp_tests/test-ETaccess.R b/nCompiler/tests/testthat/cpp_tests/test-ETaccess.R
index da66e81e..90ee616a 100644
--- a/nCompiler/tests/testthat/cpp_tests/test-ETaccess.R
+++ b/nCompiler/tests/testthat/cpp_tests/test-ETaccess.R
@@ -653,3 +653,68 @@ test_that("access and ETaccess work for logicals", {
   expect_error    (obj$LM_get_set_arg_map_scalar(LM))
   expect_identical(obj$LM_get_set_arg_map_scalar(matrix(LS)), !LS)
 })
+
+test_that("ETaccess<true> copies data and isolates from original", {
+  nc <- nClass(
+    Cpublic = list(
+      # Scalar: reading from copy gives correct value
+      DS_copy_read = nFunction(
+        function(DSx = 'numericScalar') {
+          cppLiteral('return ETaccess<true>(DSx).scalar();')
+          returnType('numericScalar')
+        }
+      ),
+      # Scalar: writing to copy does not affect original
+      DS_copy_isolation = nFunction(
+        function(DSx = 'numericScalar') {
+          cppLiteral('{ auto acc = ETaccess<true>(DSx); acc.scalar() = 99.0; }')
+          cppLiteral('return ETaccess(DSx).scalar();')
+          returnType('numericScalar')
+        }
+      ),
+      # Vector: reading from copy gives correct value
+      DV_copy_read = nFunction(
+        function(DVx = 'numericVector') {
+          cppLiteral('ans = ETaccess<true>(DVx).map<1>();', types = list(ans = 'numericVector'))
+          cppLiteral('return ans;')
+          returnType('numericVector')
+        }
+      ),
+      # Vector: writing to copy does not affect original
+      DV_copy_isolation = nFunction(
+        function(DVx = 'numericVector') {
+          cppLiteral('{ auto acc = ETaccess<true>(DVx); acc.map<1>() = acc.map<1>() * 0.0; }')
+          cppLiteral('return ETaccess(DVx).map<1>();')
+          returnType('numericVector')
+        }
+      ),
+      # Vector: copy is constructed from a lazy expression
+      DV_copy_expr = nFunction(
+        function(DVx = 'numericVector') {
+          cppLiteral('ans = ETaccess<true, Eigen::Tensor<double,1>>(DVx * 2.0).map<1>();',
+                     types = list(ans = 'numericVector'))
+          cppLiteral('return ans;')
+          returnType('numericVector')
+        }
+      )
+    )
+  )
+  Cnc <- nCompile(nc)
+  obj <- Cnc$new()
+  DS <- 1.23456
+  DV <- DS * 1:3
+
+  # Scalar copy reads the correct initial value
+  expect_equal(obj$DS_copy_read(DS), DS)
+  # Scalar copy modification leaves the original unchanged
+  expect_equal(obj$DS_copy_isolation(DS), DS)
+
+  # Vector copy reads the correct initial values
+  expect_equal(obj$DV_copy_read(DV), DV)
+  # Vector copy modification leaves the original unchanged
+  expect_equal(obj$DV_copy_isolation(DV), DV)
+
+  # Lazy expression is evaluated into the copy; original is not involved
+  expect_equal(obj$DV_copy_expr(DV), DV * 2)
+  rm(obj); gc()
+})