From 240b728d813b52a9b616b1060f8fb52837ddb0c1 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@fb.com>
Date: Wed, 18 Jan 2023 11:16:48 +1300
Subject: [PATCH] Report an error on overflow

---
 include/fmt/chrono.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/fmt/chrono.h b/include/fmt/chrono.h
index 680d829e..0a917d41 100644
--- a/include/fmt/chrono.h
+++ b/include/fmt/chrono.h
@@ -2109,8 +2109,11 @@ struct formatter<std::chrono::time_point<std::chrono::system_clock, Duration>,
           epoch - std::chrono::duration_cast<std::chrono::seconds>(epoch));
 
       if (subsecs.count() < 0) {
-        subsecs += std::chrono::seconds(1);
-        val -= std::chrono::seconds(1);
+        auto second = std::chrono::seconds(1);
+        if (epoch.count() < (Duration::min() + second).count())
+          FMT_THROW(format_error("duration is too small"));
+        subsecs += second;
+        val -= second;
       }
 
       return formatter<std::tm, Char>::do_format(