From 0c37b9ed01eea0f9455aa3583dca4cd0559da1af Mon Sep 17 00:00:00 2001
From: Brian Ward <bward@flatironinstitute.org>
Date: Thu, 3 Sep 2026 10:10:11 -0400
Subject: [PATCH] stan_csv_reader: avoid infinite loops on poorly placed EOF

---
 src/stan/io/stan_csv_reader.hpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/stan/io/stan_csv_reader.hpp b/src/stan/io/stan_csv_reader.hpp
index 4b5b217c793..c4ff05ed379 100644
--- a/src/stan/io/stan_csv_reader.hpp
+++ b/src/stan/io/stan_csv_reader.hpp
@@ -104,9 +104,9 @@ class stan_csv_reader {
     std::stringstream ss;
     std::string line;
 
-    if (in.peek() != '#')
+    if (in.peek() != '#' || !in.good())
       return;
-    while (in.peek() == '#') {
+    while (in.peek() == '#' && in.good()) {
       std::getline(in, line);
       ss << line << '\n';
     }
@@ -225,7 +225,7 @@ class stan_csv_reader {
     int lines = 0;
     if (in.peek() != '#' || in.good() == false)
       return;
-    while (in.peek() == '#') {
+    while (in.peek() == '#' && in.good()) {
       std::getline(in, line);
       ss << line << std::endl;
       lines++;