From 2ef74cb41a31dcd03b39dd5e9bf8b340669f48a4 Mon Sep 17 00:00:00 2001
From: Howard Hinnant <howard.hinnant@gmail.com>
Date: Fri, 16 Apr 2021 15:15:45 -0400
Subject: [PATCH] If %I is used without %p, mark the ambiguity with failbit

---
 include/date/date.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/date/date.h b/include/date/date.h
index 1e534f6..7b6b4e4 100644
--- a/include/date/date.h
+++ b/include/date/date.h
@@ -7845,6 +7845,8 @@ from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,
                             goto broken;
                         }
                     }
+                    else  // I is ambiguous, AM or PM?
+                        goto broken;
                 }
             }
             if (H != not_a_hour)