diff --git a/inst/include/cpp11/doubles.hpp b/inst/include/cpp11/doubles.hpp
index f15cbf07..45e3c89f 100644
--- a/inst/include/cpp11/doubles.hpp
+++ b/inst/include/cpp11/doubles.hpp
@@ -44,10 +44,16 @@ inline typename r_vector<double>::underlying_type* r_vector<double>::get_p(bool
 }
 
 template <>
-inline void r_vector<double>::const_iterator::fill_buf(R_xlen_t pos) {
-  length_ = std::min(64_xl, data_->size() - pos);
-  REAL_GET_REGION(data_->data_, pos, length_, buf_.data());
-  block_start_ = pos;
+inline void r_vector<double>::get_region(
+    SEXP x, R_xlen_t i, R_xlen_t n,
+    typename traits::get_underlying_type<double>::type* buf) {
+  // NOPROTECT: likely too costly to unwind protect here
+  REAL_GET_REGION(x, i, n, buf);
+};
+
+template <>
+inline bool r_vector<double>::const_iterator::use_buf(bool is_altrep) {
+  return is_altrep;
 }
 
 typedef r_vector<double> doubles;
diff --git a/inst/include/cpp11/integers.hpp b/inst/include/cpp11/integers.hpp
index 3bf25203..fba42669 100644
--- a/inst/include/cpp11/integers.hpp
+++ b/inst/include/cpp11/integers.hpp
@@ -45,10 +45,16 @@ inline typename r_vector<int>::underlying_type* r_vector<int>::get_p(bool is_alt
 }
 
 template <>
-inline void r_vector<int>::const_iterator::fill_buf(R_xlen_t pos) {
-  length_ = std::min(64_xl, data_->size() - pos);
-  INTEGER_GET_REGION(data_->data_, pos, length_, buf_.data());
-  block_start_ = pos;
+inline void r_vector<int>::get_region(
+    SEXP x, R_xlen_t i, R_xlen_t n,
+    typename traits::get_underlying_type<int>::type* buf) {
+  // NOPROTECT: likely too costly to unwind protect here
+  INTEGER_GET_REGION(x, i, n, buf);
+};
+
+template <>
+inline bool r_vector<int>::const_iterator::use_buf(bool is_altrep) {
+  return is_altrep;
 }
 
 typedef r_vector<int> integers;
diff --git a/inst/include/cpp11/list.hpp b/inst/include/cpp11/list.hpp
index 89c837a5..1f9d09d4 100644
--- a/inst/include/cpp11/list.hpp
+++ b/inst/include/cpp11/list.hpp
@@ -50,8 +50,15 @@ inline typename r_vector<SEXP>::underlying_type* r_vector<SEXP>::get_p(bool, SEX
 }
 
 template <>
-inline void r_vector<SEXP>::const_iterator::fill_buf(R_xlen_t) {
-  return;
+inline void r_vector<SEXP>::get_region(
+    SEXP x, R_xlen_t i, R_xlen_t n,
+    typename traits::get_underlying_type<SEXP>::type* buf) {
+  cpp11::stop("Unreachable!");
+};
+
+template <>
+inline bool r_vector<SEXP>::const_iterator::use_buf(bool is_altrep) {
+  return false;
 }
 
 template <>
diff --git a/inst/include/cpp11/logicals.hpp b/inst/include/cpp11/logicals.hpp
index 99f5204c..ec392583 100644
--- a/inst/include/cpp11/logicals.hpp
+++ b/inst/include/cpp11/logicals.hpp
@@ -43,10 +43,16 @@ inline typename r_vector<r_bool>::underlying_type* r_vector<r_bool>::get_p(bool
 }
 
 template <>
-inline void r_vector<r_bool>::const_iterator::fill_buf(R_xlen_t pos) {
-  length_ = std::min(64_xl, data_->size() - pos);
-  LOGICAL_GET_REGION(data_->data_, pos, length_, buf_.data());
-  block_start_ = pos;
+inline void r_vector<r_bool>::get_region(
+    SEXP x, R_xlen_t i, R_xlen_t n,
+    typename traits::get_underlying_type<r_bool>::type* buf) {
+  // NOPROTECT: likely too costly to unwind protect here
+  LOGICAL_GET_REGION(x, i, n, buf);
+};
+
+template <>
+inline bool r_vector<r_bool>::const_iterator::use_buf(bool is_altrep) {
+  return is_altrep;
 }
 
 typedef r_vector<r_bool> logicals;
diff --git a/inst/include/cpp11/r_vector.hpp b/inst/include/cpp11/r_vector.hpp
index 44cca1e6..ea6bf4b3 100644
--- a/inst/include/cpp11/r_vector.hpp
+++ b/inst/include/cpp11/r_vector.hpp
@@ -138,6 +138,7 @@ class r_vector {
 
    private:
     /// Implemented in specialization
+    static bool use_buf(bool is_altrep);
     void fill_buf(R_xlen_t pos);
   };
 
@@ -145,6 +146,8 @@ class r_vector {
   /// Implemented in specialization
   static underlying_type* get_p(bool is_altrep, SEXP data);
   /// Implemented in specialization
+  static void get_region(SEXP x, R_xlen_t i, R_xlen_t n, underlying_type* buf);
+  /// Implemented in specialization
   static SEXP valid_type(SEXP data);
 
   friend class writable::r_vector<T>;
@@ -283,6 +286,7 @@ class r_vector : public cpp11::r_vector<T> {
     using cpp11::r_vector<T>::const_iterator::pos_;
     using cpp11::r_vector<T>::const_iterator::buf_;
     using cpp11::r_vector<T>::const_iterator::length_;
+    using cpp11::r_vector<T>::const_iterator::use_buf;
     using cpp11::r_vector<T>::const_iterator::fill_buf;
 
    public:
@@ -572,7 +576,7 @@ inline typename r_vector<T>::const_iterator r_vector<T>::cend() const {
 template <typename T>
 r_vector<T>::const_iterator::const_iterator(const r_vector* data, R_xlen_t pos)
     : data_(data), pos_(pos), buf_() {
-  if (data_->is_altrep()) {
+  if (use_buf(data_->is_altrep())) {
     fill_buf(pos);
   }
 }
@@ -580,7 +584,7 @@ r_vector<T>::const_iterator::const_iterator(const r_vector* data, R_xlen_t pos)
 template <typename T>
 inline typename r_vector<T>::const_iterator& r_vector<T>::const_iterator::operator++() {
   ++pos_;
-  if (data_->is_altrep() && pos_ >= block_start_ + length_) {
+  if (use_buf(data_->is_altrep()) && pos_ >= block_start_ + length_) {
     fill_buf(pos_);
   }
   return *this;
@@ -589,7 +593,7 @@ inline typename r_vector<T>::const_iterator& r_vector<T>::const_iterator::operat
 template <typename T>
 inline typename r_vector<T>::const_iterator& r_vector<T>::const_iterator::operator--() {
   --pos_;
-  if (data_->is_altrep() && pos_ > 0 && pos_ < block_start_) {
+  if (use_buf(data_->is_altrep()) && pos_ > 0 && pos_ < block_start_) {
     fill_buf(std::max(0_xl, pos_ - 64));
   }
   return *this;
@@ -599,7 +603,7 @@ template <typename T>
 inline typename r_vector<T>::const_iterator& r_vector<T>::const_iterator::operator+=(
     R_xlen_t i) {
   pos_ += i;
-  if (data_->is_altrep() && pos_ >= block_start_ + length_) {
+  if (use_buf(data_->is_altrep()) && pos_ >= block_start_ + length_) {
     fill_buf(pos_);
   }
   return *this;
@@ -609,7 +613,7 @@ template <typename T>
 inline typename r_vector<T>::const_iterator& r_vector<T>::const_iterator::operator-=(
     R_xlen_t i) {
   pos_ -= i;
-  if (data_->is_altrep() && pos_ >= block_start_ + length_) {
+  if (use_buf(data_->is_altrep()) && pos_ >= block_start_ + length_) {
     fill_buf(std::max(0_xl, pos_ - 64));
   }
   return *this;
@@ -666,6 +670,14 @@ inline T r_vector<T>::const_iterator::operator*() const {
   }
 }
 
+template <typename T>
+inline void r_vector<T>::const_iterator::fill_buf(R_xlen_t pos) {
+  using namespace cpp11::literals;
+  length_ = std::min(64_xl, data_->size() - pos);
+  get_region(data_->data_, pos, length_, buf_.data());
+  block_start_ = pos;
+}
+
 namespace writable {
 
 template <typename T>
@@ -1062,7 +1074,7 @@ r_vector<T>::iterator::iterator(const r_vector& data, R_xlen_t pos)
 template <typename T>
 inline typename r_vector<T>::iterator& r_vector<T>::iterator::operator++() {
   ++pos_;
-  if (data_.is_altrep() && pos_ >= block_start_ + length_) {
+  if (use_buf(data_.is_altrep()) && pos_ >= block_start_ + length_) {
     fill_buf(pos_);
   }
   return *this;
@@ -1070,7 +1082,7 @@ inline typename r_vector<T>::iterator& r_vector<T>::iterator::operator++() {
 
 template <typename T>
 inline typename r_vector<T>::proxy r_vector<T>::iterator::operator*() const {
-  if (data_.is_altrep()) {
+  if (use_buf(data_.is_altrep())) {
     return proxy(
         data_.data(), pos_,
         const_cast<typename r_vector::underlying_type*>(&buf_[pos_ - block_start_]),
@@ -1084,7 +1096,7 @@ inline typename r_vector<T>::proxy r_vector<T>::iterator::operator*() const {
 template <typename T>
 inline typename r_vector<T>::iterator& r_vector<T>::iterator::operator+=(R_xlen_t rhs) {
   pos_ += rhs;
-  if (data_.is_altrep() && pos_ >= block_start_ + length_) {
+  if (use_buf(data_.is_altrep()) && pos_ >= block_start_ + length_) {
     fill_buf(pos_);
   }
   return *this;
diff --git a/inst/include/cpp11/raws.hpp b/inst/include/cpp11/raws.hpp
index c6705bcb..9f198066 100644
--- a/inst/include/cpp11/raws.hpp
+++ b/inst/include/cpp11/raws.hpp
@@ -52,11 +52,16 @@ inline typename r_vector<uint8_t>::underlying_type* r_vector<uint8_t>::get_p(
 }
 
 template <>
-inline void r_vector<uint8_t>::const_iterator::fill_buf(R_xlen_t pos) {
-  using namespace cpp11::literals;
-  length_ = std::min(64_xl, data_->size() - pos);
-  unwind_protect([&] { RAW_GET_REGION(data_->data_, pos, length_, buf_.data()); });
-  block_start_ = pos;
+inline void r_vector<uint8_t>::get_region(
+    SEXP x, R_xlen_t i, R_xlen_t n,
+    typename traits::get_underlying_type<uint8_t>::type* buf) {
+  // NOPROTECT: likely too costly to unwind protect here
+  RAW_GET_REGION(x, i, n, buf);
+};
+
+template <>
+inline bool r_vector<uint8_t>::const_iterator::use_buf(bool is_altrep) {
+  return is_altrep;
 }
 
 typedef r_vector<uint8_t> raws;
diff --git a/inst/include/cpp11/strings.hpp b/inst/include/cpp11/strings.hpp
index 64cee045..d7dcd0a2 100644
--- a/inst/include/cpp11/strings.hpp
+++ b/inst/include/cpp11/strings.hpp
@@ -40,8 +40,15 @@ inline typename r_vector<r_string>::underlying_type* r_vector<r_string>::get_p(b
 }
 
 template <>
-inline void r_vector<r_string>::const_iterator::fill_buf(R_xlen_t) {
-  return;
+inline void r_vector<r_string>::get_region(
+    SEXP x, R_xlen_t i, R_xlen_t n,
+    typename traits::get_underlying_type<r_string>::type* buf) {
+  cpp11::stop("Unreachable!");
+};
+
+template <>
+inline bool r_vector<r_string>::const_iterator::use_buf(bool is_altrep) {
+  return false;
 }
 
 template <>