diff --git a/R/model.R b/R/model.R
index 2a7b4623f..5fe9f70fc 100644
--- a/R/model.R
+++ b/R/model.R
@@ -230,7 +230,7 @@ CmdStanModel <- R6::R6Class(
       self$functions <- new.env()
       self$functions$compiled <- FALSE
       if (!is.null(stan_file)) {
-        assert_file_exists(stan_file, access = "r", extension = "stan")
+        assert_file_exists(stan_file, access = "r", extension = c("stan", "stanfunctions"))
         checkmate::assert_flag(compile)
         private$stan_file_ <- absolute_path(stan_file)
         private$stan_code_ <- readLines(stan_file)
@@ -537,7 +537,7 @@ compile <- function(quiet = TRUE,
     compile_hessian_method <- FALSE
   }
 
-  temp_stan_file <- tempfile(pattern = "model-", fileext = ".stan")
+  temp_stan_file <- tempfile(pattern = "model-", fileext = paste0(".", tools::file_ext(self$stan_file())))
   file.copy(self$stan_file(), temp_stan_file, overwrite = TRUE)
   temp_file_no_ext <- strip_ext(temp_stan_file)
   tmp_exe <- cmdstan_ext(temp_file_no_ext) # adds .exe on Windows
diff --git a/R/utils.R b/R/utils.R
index 96c7739cf..d270cef7f 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -748,7 +748,8 @@ expose_model_methods <- function(env, verbose = FALSE, hessian = FALSE) {
                                   package = "cmdstanr", mustWork = TRUE)))
 
   if (hessian) {
-    code <- c(code,
+    code <- c("#include <stan/math/mix.hpp>",
+            code,
             readLines(system.file("include", "hessian.cpp",
                                   package = "cmdstanr", mustWork = TRUE)))
   }
@@ -758,9 +759,8 @@ expose_model_methods <- function(env, verbose = FALSE, hessian = FALSE) {
   invisible(NULL)
 }
 
-initialize_model_pointer <- function(env, data, seed = 0) {
-  datafile_path <- ifelse(is.null(data), "", data)
-  ptr_and_rng <- env$model_ptr(datafile_path, seed)
+initialize_model_pointer <- function(env, datafile_path, seed = 0) {
+  ptr_and_rng <- env$model_ptr(ifelse(is.null(datafile_path), "", datafile_path), seed)
   env$model_ptr_ <- ptr_and_rng$model_ptr
   env$model_rng_ <- ptr_and_rng$base_rng
   env$num_upars_ <- env$get_num_upars(env$model_ptr_)
@@ -863,8 +863,8 @@ prep_fun_cpp <- function(fun_start, fun_end, model_lines) {
   fun_body <- gsub("auto", get_plain_rtn(fun_start, fun_end, model_lines), fun_body)
   fun_body <- gsub("// [[stan::function]]", "// [[Rcpp::export]]\n", fun_body, fixed = TRUE)
   fun_body <- gsub("std::ostream\\*\\s*pstream__\\s*=\\s*nullptr", "", fun_body)
-  fun_body <- gsub("boost::ecuyer1988& base_rng__", "size_t seed = 0", fun_body, fixed = TRUE)
-  fun_body <- gsub("base_rng__,", "*(new boost::ecuyer1988(seed)),", fun_body, fixed = TRUE)
+  fun_body <- gsub("boost::ecuyer1988&\\s*base_rng__", "SEXP base_rng_ptr", fun_body)
+  fun_body <- gsub("base_rng__,", "*(Rcpp::XPtr<boost::ecuyer1988>(base_rng_ptr).get()),", fun_body, fixed = TRUE)
   fun_body <- gsub("pstream__", "&Rcpp::Rcout", fun_body, fixed = TRUE)
   fun_body <- paste(fun_body, collapse = "\n")
   gsub(pattern = ",\\s*)", replacement = ")", fun_body)
@@ -904,6 +904,30 @@ compile_functions <- function(env, verbose = FALSE, global = FALSE) {
   } else {
     rcpp_source_stan(mod_stan_funs, env, verbose)
   }
+
+  # If an RNG function is exposed, initialise a Boost RNG object stored in the
+  # environment
+  rng_funs <- grep("rng\\b", env$fun_names, value = TRUE)
+  if (length(rng_funs) > 0) {
+    rng_cpp <- system.file("include", "base_rng.cpp", package = "cmdstanr", mustWork = TRUE)
+    rcpp_source_stan(paste0(readLines(rng_cpp), collapse="\n"), env, verbose)
+    env$rng_ptr <- env$base_rng(seed=0)
+  }
+
+  # For all RNG functions, pass the initialised Boost RNG by default
+  for (fun in rng_funs) {
+    if (global) {
+      fun_env <- globalenv()
+    } else {
+      fun_env <- env
+    }
+    fundef <- get(fun, envir = fun_env)
+    funargs <- formals(fundef)
+    funargs$base_rng_ptr <- env$rng_ptr
+    formals(fundef) <- funargs
+    assign(fun, fundef, envir = fun_env)
+  }
+
   env$compiled <- TRUE
   invisible(NULL)
 }
diff --git a/inst/include/base_rng.cpp b/inst/include/base_rng.cpp
new file mode 100644
index 000000000..7b38ba16f
--- /dev/null
+++ b/inst/include/base_rng.cpp
@@ -0,0 +1,8 @@
+#include <Rcpp.h>
+#include <boost/random/additive_combine.hpp>
+
+// [[Rcpp::export]]
+SEXP base_rng(boost::uint32_t seed = 0) {
+  Rcpp::XPtr<boost::ecuyer1988> rng_ptr(new boost::ecuyer1988(seed));
+  return rng_ptr;
+}
diff --git a/tests/testthat/test-model-expose-functions.R b/tests/testthat/test-model-expose-functions.R
index 9836d4065..e1e99d1bb 100644
--- a/tests/testthat/test-model-expose-functions.R
+++ b/tests/testthat/test-model-expose-functions.R
@@ -112,7 +112,7 @@ test_that("Functions can be compiled with model", {
 
 test_that("rng functions can be exposed", {
   skip_if(os_is_wsl())
-  function_decl <- "functions { real normal_rng(real mu) { return normal_rng(mu, 1); } }"
+  function_decl <- "functions { real wrap_normal_rng(real mu, real sigma) { return normal_rng(mu, sigma); } }"
   stan_prog <- paste(function_decl,
                      paste(readLines(testing_stan_file("bernoulli")),
                            collapse = "\n"),
@@ -122,11 +122,17 @@ test_that("rng functions can be exposed", {
   mod <- cmdstan_model(model, force_recompile = TRUE)
   fit <- mod$sample(data = data_list)
 
+  set.seed(10)
   fit$expose_functions(verbose = TRUE)
 
   expect_equal(
-    fit$functions$normal_rng(5, seed = 10),
-    3.8269637967017344771
+    fit$functions$wrap_normal_rng(5,10),
+    -4.5298764235381225873
+  )
+
+  expect_equal(
+    fit$functions$wrap_normal_rng(5,10),
+    8.1295902610102039887
   )
 })