diff --git a/inst/include/cpp11/doubles.hpp b/inst/include/cpp11/doubles.hpp
index 44d24bca..824c294c 100644
--- a/inst/include/cpp11/doubles.hpp
+++ b/inst/include/cpp11/doubles.hpp
@@ -54,6 +54,11 @@ typedef r_vector<double> doubles;
 
 namespace writable {
 
+template <>
+inline SEXPTYPE r_vector<double>::get_sexptype() {
+  return REALSXP;
+}
+
 template <>
 inline typename r_vector<double>::proxy& r_vector<double>::proxy::operator=(
     const double& rhs) {
@@ -104,18 +109,6 @@ inline r_vector<double>::r_vector(std::initializer_list<named_arg> il)
   }
 }
 
-template <>
-inline void r_vector<double>::reserve(R_xlen_t new_capacity) {
-  data_ = data_ == R_NilValue ? safe[Rf_allocVector](REALSXP, new_capacity)
-                              : safe[Rf_xlengthgets](data_, new_capacity);
-  SEXP old_protect = protect_;
-  protect_ = detail::store::insert(data_);
-  detail::store::release(old_protect);
-
-  data_p_ = REAL(data_);
-  capacity_ = new_capacity;
-}
-
 template <>
 inline void r_vector<double>::push_back(double value) {
   while (length_ >= capacity_) {
diff --git a/inst/include/cpp11/integers.hpp b/inst/include/cpp11/integers.hpp
index 97f2c6a7..6e7ac8d7 100644
--- a/inst/include/cpp11/integers.hpp
+++ b/inst/include/cpp11/integers.hpp
@@ -55,6 +55,11 @@ typedef r_vector<int> integers;
 
 namespace writable {
 
+template <>
+inline SEXPTYPE r_vector<int>::get_sexptype() {
+  return INTSXP;
+}
+
 template <>
 inline typename r_vector<int>::proxy& r_vector<int>::proxy::operator=(const int& rhs) {
   if (is_altrep_) {
@@ -80,22 +85,6 @@ template <>
 inline r_vector<int>::r_vector(std::initializer_list<int> il)
     : cpp11::r_vector<int>(as_sexp(il)), capacity_(il.size()) {}
 
-template <>
-inline void r_vector<int>::reserve(R_xlen_t new_capacity) {
-  data_ = data_ == R_NilValue ? safe[Rf_allocVector](INTSXP, new_capacity)
-                              : safe[Rf_xlengthgets](data_, new_capacity);
-  SEXP old_protect = protect_;
-
-  // Protect the new data
-  protect_ = detail::store::insert(data_);
-
-  // Release the old protection;
-  detail::store::release(old_protect);
-
-  data_p_ = INTEGER(data_);
-  capacity_ = new_capacity;
-}
-
 template <>
 inline r_vector<int>::r_vector(std::initializer_list<named_arg> il)
     : cpp11::r_vector<int>(safe[Rf_allocVector](INTSXP, il.size())),
diff --git a/inst/include/cpp11/list.hpp b/inst/include/cpp11/list.hpp
index 3f258a65..2ee745e6 100644
--- a/inst/include/cpp11/list.hpp
+++ b/inst/include/cpp11/list.hpp
@@ -63,6 +63,11 @@ typedef r_vector<SEXP> list;
 
 namespace writable {
 
+template <>
+inline SEXPTYPE r_vector<SEXP>::get_sexptype() {
+  return VECSXP;
+}
+
 template <>
 inline typename r_vector<SEXP>::proxy& r_vector<SEXP>::proxy::operator=(const SEXP& rhs) {
   SET_VECTOR_ELT(data_, index_, rhs);
@@ -108,18 +113,6 @@ inline r_vector<SEXP>::r_vector(std::initializer_list<named_arg> il)
   }
 }
 
-template <>
-inline void r_vector<SEXP>::reserve(R_xlen_t new_capacity) {
-  data_ = data_ == R_NilValue ? safe[Rf_allocVector](VECSXP, new_capacity)
-                              : safe[Rf_xlengthgets](data_, new_capacity);
-
-  SEXP old_protect = protect_;
-  protect_ = detail::store::insert(data_);
-  detail::store::release(old_protect);
-
-  capacity_ = new_capacity;
-}
-
 template <>
 inline void r_vector<SEXP>::push_back(SEXP value) {
   while (length_ >= capacity_) {
diff --git a/inst/include/cpp11/logicals.hpp b/inst/include/cpp11/logicals.hpp
index 076135a5..7fe94bf5 100644
--- a/inst/include/cpp11/logicals.hpp
+++ b/inst/include/cpp11/logicals.hpp
@@ -53,6 +53,11 @@ typedef r_vector<r_bool> logicals;
 
 namespace writable {
 
+template <>
+inline SEXPTYPE r_vector<r_bool>::get_sexptype() {
+  return LGLSXP;
+}
+
 template <>
 inline typename r_vector<r_bool>::proxy& r_vector<r_bool>::proxy::operator=(
     const r_bool& rhs) {
@@ -110,19 +115,6 @@ inline r_vector<r_bool>::r_vector(std::initializer_list<named_arg> il)
   }
 }
 
-template <>
-inline void r_vector<r_bool>::reserve(R_xlen_t new_capacity) {
-  data_ = data_ == R_NilValue ? safe[Rf_allocVector](LGLSXP, new_capacity)
-                              : safe[Rf_xlengthgets](data_, new_capacity);
-  SEXP old_protect = protect_;
-  protect_ = detail::store::insert(data_);
-
-  detail::store::release(old_protect);
-
-  data_p_ = LOGICAL(data_);
-  capacity_ = new_capacity;
-}
-
 template <>
 inline void r_vector<r_bool>::push_back(r_bool value) {
   while (length_ >= capacity_) {
diff --git a/inst/include/cpp11/r_vector.hpp b/inst/include/cpp11/r_vector.hpp
index 198a769b..c4b22ee4 100644
--- a/inst/include/cpp11/r_vector.hpp
+++ b/inst/include/cpp11/r_vector.hpp
@@ -228,8 +228,6 @@ class r_vector : public cpp11::r_vector<T> {
   void pop_back();
 
   void resize(R_xlen_t count);
-
-  /// Implemented in specialization
   void reserve(R_xlen_t new_capacity);
 
   iterator insert(R_xlen_t pos, T value);
@@ -308,6 +306,9 @@ class r_vector : public cpp11::r_vector<T> {
   };
 
  private:
+  /// Implemented in specialization
+  static SEXPTYPE get_sexptype();
+
   using cpp11::r_vector<T>::get_p;
 };
 }  // namespace writable
@@ -886,6 +887,26 @@ inline void r_vector<T>::resize(R_xlen_t count) {
   length_ = count;
 }
 
+/// Reserve a new capacity and copy all elements over
+///
+/// SAFETY: The new capacity is allowed to be smaller than the current capacity, which
+/// is used in the `SEXP` conversion operator during truncation, but if that occurs then
+/// we also need to update the `length_`, so if you need to truncate then you should call
+/// `resize()` instead.
+template <typename T>
+inline void r_vector<T>::reserve(R_xlen_t new_capacity) {
+  SEXP old_protect = protect_;
+
+  data_ = (data_ == R_NilValue) ? safe[Rf_allocVector](get_sexptype(), new_capacity)
+                                : safe[Rf_xlengthgets](data_, new_capacity);
+  protect_ = detail::store::insert(data_);
+  is_altrep_ = ALTREP(data_);
+  data_p_ = get_p(is_altrep_, data_);
+  capacity_ = new_capacity;
+
+  detail::store::release(old_protect);
+}
+
 template <typename T>
 inline typename r_vector<T>::iterator r_vector<T>::insert(R_xlen_t pos, T value) {
   push_back(value);
diff --git a/inst/include/cpp11/raws.hpp b/inst/include/cpp11/raws.hpp
index 419ce63f..531b6d0f 100644
--- a/inst/include/cpp11/raws.hpp
+++ b/inst/include/cpp11/raws.hpp
@@ -62,6 +62,11 @@ typedef r_vector<uint8_t> raws;
 
 namespace writable {
 
+template <>
+inline SEXPTYPE r_vector<uint8_t>::get_sexptype() {
+  return RAWSXP;
+}
+
 template <>
 inline typename r_vector<uint8_t>::proxy& r_vector<uint8_t>::proxy::operator=(
     const uint8_t& rhs) {
@@ -119,19 +124,6 @@ inline r_vector<uint8_t>::r_vector(std::initializer_list<named_arg> il)
   }
 }
 
-template <>
-inline void r_vector<uint8_t>::reserve(R_xlen_t new_capacity) {
-  data_ = data_ == R_NilValue ? safe[Rf_allocVector](RAWSXP, new_capacity)
-                              : safe[Rf_xlengthgets](data_, new_capacity);
-
-  SEXP old_protect = protect_;
-  protect_ = detail::store::insert(data_);
-  detail::store::release(old_protect);
-
-  data_p_ = RAW(data_);
-  capacity_ = new_capacity;
-}
-
 template <>
 inline void r_vector<uint8_t>::push_back(uint8_t value) {
   while (length_ >= capacity_) {
diff --git a/inst/include/cpp11/strings.hpp b/inst/include/cpp11/strings.hpp
index 2e1390e0..c121b039 100644
--- a/inst/include/cpp11/strings.hpp
+++ b/inst/include/cpp11/strings.hpp
@@ -53,6 +53,11 @@ typedef r_vector<r_string> strings;
 
 namespace writable {
 
+template <>
+inline SEXPTYPE r_vector<r_string>::get_sexptype() {
+  return STRSXP;
+}
+
 template <>
 inline typename r_vector<r_string>::proxy& r_vector<r_string>::proxy::operator=(
     const r_string& rhs) {
@@ -136,18 +141,6 @@ inline r_vector<r_string>::r_vector(std::initializer_list<named_arg> il)
   }
 }
 
-template <>
-inline void r_vector<r_string>::reserve(R_xlen_t new_capacity) {
-  data_ = data_ == R_NilValue ? safe[Rf_allocVector](STRSXP, new_capacity)
-                              : safe[Rf_xlengthgets](data_, new_capacity);
-
-  SEXP old_protect = protect_;
-  protect_ = detail::store::insert(data_);
-  detail::store::release(old_protect);
-
-  capacity_ = new_capacity;
-}
-
 template <>
 inline void r_vector<r_string>::push_back(r_string value) {
   while (length_ >= capacity_) {