diff --git a/stl/inc/chrono b/stl/inc/chrono
index 6c82f5177d..1dfd8d6a3b 100644
--- a/stl/inc/chrono
+++ b/stl/inc/chrono
@@ -4212,8 +4212,8 @@ namespace chrono {
             char _Ch;
             while (_First != _Last && _Width > 0 && '0' <= (_Ch = _Ctype_fac.narrow(*_First))
                    && _Ch <= '9') { // copy digits
-                *_Ptr = _Ch;
-                if (_Ptr < _STD cend(_Ac)) {
+                if (_Ptr < _STD cend(_Ac) - 1) { // preserve room for the null terminator written below
+                    *_Ptr = _Ch;
                     ++_Ptr; // drop trailing digits if already too large
                 }
                 ++_First;
diff --git a/stl/inc/xloctime b/stl/inc/xloctime
index 01e9697fd5..f86e4aa0af 100644
--- a/stl/inc/xloctime
+++ b/stl/inc/xloctime
@@ -57,8 +57,8 @@ ios_base::iostate _Getint_v2(_InIt& _First, _InIt& _Last, int _Lo, int _Hi, int&
     for (char* const _Pe = &_Ac[_Max_int_dig - 1];
         _First != _Last && '0' <= (_Ch = _Ctype_fac.narrow(*_First)) && _Ch <= '9' && _Digits_read < _Hi_digits;
         ++_Digits_read, (void) ++_First) { // copy digits
-        *_Ptr = _Ch;
-        if (_Ptr < _Pe) {
+        if (_Ptr < _Pe) { // preserve room for the null terminator written below
+            *_Ptr = _Ch;
             ++_Ptr; // drop trailing digits if already too large
         }
     }
diff --git a/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp b/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp
index 8ee6020e17..9d26f33b46 100644
--- a/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp
+++ b/tests/std/tests/P0355R7_calendars_and_time_zones_io/test.cpp
@@ -6,11 +6,13 @@
 #include <charconv>
 #include <chrono>
 #include <cstdint>
+#include <cstdio>
 #include <istream>
 #include <iterator>
 #include <limits>
 #include <locale>
 #include <ratio>
+#include <source_location>
 #include <sstream>
 #include <string>
 #include <type_traits>
@@ -36,7 +38,7 @@ bool test_duration_basic_out(const duration<Rep, Period>& d, const CharT* expect
 
 template <class CharT>
 bool test_duration_locale_out() {
-    basic_stringstream<CharT> ss;
+    basic_ostringstream<CharT> ss;
     const duration<double> d{0.140625};
     ss.precision(3);
     ss << d;
@@ -153,7 +155,7 @@ ios_base::iostate parse_state(const CharT* str, const CStringOrStdString& fmt, P
         *offset = minutes::min();
     }
 
-    basic_stringstream<CharT> sstr{str};
+    basic_istringstream<CharT> sstr{str};
     if (abbrev) {
         if (offset) {
             sstr >> parse(fmt, p, *abbrev, *offset);
@@ -173,14 +175,40 @@ ios_base::iostate parse_state(const CharT* str, const CStringOrStdString& fmt, P
 
 template <class CharT, class CStringOrStdString, class Parsable>
 void test_parse(const CharT* str, const CStringOrStdString& fmt, Parsable& p,
-    type_identity_t<basic_string<CharT>*> abbrev = nullptr, minutes* offset = nullptr) {
-    assert((parse_state(str, fmt, p, abbrev, offset) & ~ios_base::eofbit) == ios_base::goodbit);
+    type_identity_t<basic_string<CharT>*> abbrev = nullptr, minutes* offset = nullptr,
+    const source_location sl = source_location::current()) {
+    const auto masked_state = parse_state(str, fmt, p, abbrev, offset) & ~ios_base::eofbit;
+    const bool desirable    = masked_state == ios_base::goodbit;
+    if (!desirable) {
+        printf("test_parse() encountered a problem on line %u.\n", static_cast<unsigned int>(sl.line()));
+    }
+    assert(desirable);
+}
+
+template <class CharT, class CStringOrStdString, class Parsable>
+void test_parse(const basic_string<CharT>& str, const CStringOrStdString& fmt, Parsable& p,
+    type_identity_t<basic_string<CharT>*> abbrev = nullptr, minutes* offset = nullptr,
+    const source_location sl = source_location::current()) {
+    test_parse(str.c_str(), fmt, p, abbrev, offset, sl);
 }
 
 template <class CharT, class CStringOrStdString, class Parsable>
 void fail_parse(const CharT* str, const CStringOrStdString& fmt, Parsable& p,
-    type_identity_t<basic_string<CharT>*> abbrev = nullptr, minutes* offset = nullptr) {
-    assert((parse_state(str, fmt, p, abbrev, offset) & ~ios_base::eofbit) != ios_base::goodbit);
+    type_identity_t<basic_string<CharT>*> abbrev = nullptr, minutes* offset = nullptr,
+    const source_location sl = source_location::current()) {
+    const auto masked_state = parse_state(str, fmt, p, abbrev, offset) & ~ios_base::eofbit;
+    const bool desirable    = masked_state != ios_base::goodbit;
+    if (!desirable) {
+        printf("fail_parse() encountered a problem on line %u.\n", static_cast<unsigned int>(sl.line()));
+    }
+    assert(desirable);
+}
+
+template <class CharT, class CStringOrStdString, class Parsable>
+void fail_parse(const basic_string<CharT>& str, const CStringOrStdString& fmt, Parsable& p,
+    type_identity_t<basic_string<CharT>*> abbrev = nullptr, minutes* offset = nullptr,
+    const source_location sl = source_location::current()) {
+    fail_parse(str.c_str(), fmt, p, abbrev, offset, sl);
 }
 
 template <class TimeType, class IntType = int>
@@ -208,29 +236,6 @@ void test_limits(const char* flag, const IntType min, const IntType max) {
     assert(value == TimeType{max});
 }
 
-void test_lwg_3536() {
-    // LWG-3536, "Should chrono::from_stream() assign zero to duration for failure?"
-    minutes mm{20};
-
-    {
-        istringstream iss{"2:2:30"};
-        iss >> parse("%H:%M:%S", mm);
-        assert(iss.fail() && mm == 20min);
-    }
-
-    {
-        istringstream iss{"June"};
-        iss >> parse("%B", mm);
-        assert(iss.fail() && mm == 20min);
-    }
-
-    {
-        istringstream iss{""};
-        iss >> parse("%B", mm);
-        assert(iss.fail() && mm == 20min);
-    }
-}
-
 void parse_seconds() {
     seconds time;
     test_parse("1", "%S", time);
@@ -631,7 +636,7 @@ void parse_calendar_types_basic() {
     // not ambiguous with year
     year_month_day ymd;
     test_parse("60 2004-02-29", "%j %F", ymd);
-    assert(ymd == 2004y / February / 29);
+    assert(ymd == 2004y / February / 29d);
 
     // basic year_month_day tests
     // different ways of specifying year
@@ -1221,6 +1226,187 @@ void parse_timepoints() {
     assert(ut == clock_cast<utc_clock>(sys_days{1d / January / 2017y}) - 1s);
 }
 
+void parse_modified_maximum_characters() {
+    const string hundred_digits(100, '1');
+    const string seventy_zeroes(70, '0');
+
+    {
+        day d{7};
+        test_parse(hundred_digits, "%d", d);
+        assert(d == day{11});
+        fail_parse(seventy_zeroes + "22", "%d", d); // 0 is not a valid day of the month
+        fail_parse(hundred_digits, "%100d", d); // overflow
+        test_parse(seventy_zeroes + "22", "%100d", d);
+        assert(d == day{22});
+
+        test_parse(hundred_digits, "%e", d);
+        assert(d == day{11});
+        fail_parse(seventy_zeroes + "22", "%e", d); // 0 is not a valid day of the month
+        fail_parse(hundred_digits, "%100e", d); // overflow
+        test_parse(seventy_zeroes + "22", "%100e", d);
+        assert(d == day{22});
+    }
+
+    {
+        hours h{33h};
+        test_parse(hundred_digits, "%H", h);
+        assert(h == 11h);
+        test_parse(seventy_zeroes + "22", "%H", h);
+        assert(h == 0h);
+        fail_parse(hundred_digits, "%100H", h); // overflow
+        test_parse(seventy_zeroes + "22", "%100H", h);
+        assert(h == 22h);
+
+        test_parse(hundred_digits, "%I", h);
+        assert(h == 11h);
+        fail_parse(seventy_zeroes + "7", "%I", h); // 0 is not a valid 12-hour clock
+        fail_parse(hundred_digits, "%100I", h); // overflow
+        test_parse(seventy_zeroes + "7", "%100I", h);
+        assert(h == 7h);
+    }
+
+    {
+        days ds{22};
+        test_parse(hundred_digits, "%j", ds);
+        assert(ds == days{111});
+        test_parse(seventy_zeroes + "1729", "%j", ds);
+        assert(ds == days{0});
+        fail_parse(hundred_digits, "%100j", ds); // overflow
+        test_parse(seventy_zeroes + "1729", "%100j", ds);
+        assert(ds == days{1729});
+    }
+
+    {
+        year_month_day ymd{1970y / January / 1d};
+        test_parse("2030 " + hundred_digits, "%Y %j", ymd);
+        assert(ymd == 2030y / April / 21d);
+        fail_parse("2030 " + seventy_zeroes + "124", "%Y %j", ymd); // 0 is not a valid day of the year
+        fail_parse("2030 " + hundred_digits, "%Y %100j", ymd); // overflow
+        test_parse("2030 " + seventy_zeroes + "124", "%Y %100j", ymd);
+        assert(ymd == 2030y / May / 4d);
+
+        fail_parse(hundred_digits + "-02-03", "%100F", ymd); // overflow
+        test_parse(seventy_zeroes + "1969-07-20", "%100F", ymd);
+        assert(ymd == 1969y / July / 20d);
+
+        test_parse("2015 4 " + hundred_digits, "%Y %u %U", ymd);
+        assert(ymd == 2015y / March / 19d);
+        test_parse("2015 4 " + seventy_zeroes + "6", "%Y %u %U", ymd);
+        assert(ymd == 2015y / January / 1d);
+        fail_parse("2015 4 " + hundred_digits, "%Y %u %100U", ymd); // overflow
+        test_parse("2015 4 " + seventy_zeroes + "6", "%Y %u %100U", ymd);
+        assert(ymd == 2015y / February / 12d);
+
+        test_parse("2015 4 " + hundred_digits, "%Y %u %W", ymd);
+        assert(ymd == 2015y / March / 19d);
+        test_parse("2015 4 " + seventy_zeroes + "6", "%Y %u %W", ymd);
+        assert(ymd == 2015y / January / 1d);
+        fail_parse("2015 4 " + hundred_digits, "%Y %u %100W", ymd); // overflow
+        test_parse("2015 4 " + seventy_zeroes + "6", "%Y %u %100W", ymd);
+        assert(ymd == 2015y / February / 12d);
+
+        test_parse("4 03 19 " + hundred_digits, "%u %V %C %g", ymd);
+        assert(ymd == 1911y / January / 19d);
+        test_parse("4 03 19 " + seventy_zeroes + "33", "%u %V %C %g", ymd);
+        assert(ymd == 1900y / January / 18d);
+        fail_parse("4 03 19 " + hundred_digits, "%u %V %C %100g", ymd); // overflow
+        test_parse("4 03 19 " + seventy_zeroes + "55", "%u %V %C %100g", ymd);
+        assert(ymd == 1955y / January / 20d);
+
+        test_parse("4 03 " + hundred_digits, "%u %V %G", ymd);
+        assert(ymd == 1111y / January / 19d);
+        test_parse("4 03 " + seventy_zeroes + "2030", "%u %V %G", ymd);
+        assert(ymd == 0y / January / 20d);
+        fail_parse("4 03 " + hundred_digits, "%u %V %100G", ymd); // overflow
+        test_parse("4 03 " + seventy_zeroes + "2030", "%u %V %100G", ymd);
+        assert(ymd == 2030y / January / 17d);
+
+        test_parse("4 2015 " + hundred_digits, "%u %G %V", ymd);
+        assert(ymd == 2015y / March / 12d);
+        fail_parse("4 2015 " + seventy_zeroes + "33", "%u %G %V", ymd); // 0 is not a valid ISO week
+        fail_parse("4 2015 " + hundred_digits, "%u %G %100V", ymd); // overflow
+        test_parse("4 2015 " + seventy_zeroes + "33", "%u %G %100V", ymd);
+        assert(ymd == 2015y / August / 13d);
+    }
+
+    {
+        month mo{January};
+        test_parse(hundred_digits, "%m", mo);
+        assert(mo == November);
+        fail_parse(seventy_zeroes + "12", "%m", mo); // 0 is not a valid month
+        fail_parse(hundred_digits, "%100m", mo); // overflow
+        test_parse(seventy_zeroes + "12", "%100m", mo);
+        assert(mo == December);
+    }
+
+    {
+        minutes mi{22min};
+        test_parse(hundred_digits, "%M", mi);
+        assert(mi == 11min);
+        test_parse(seventy_zeroes + "55", "%M", mi);
+        assert(mi == 0min);
+        fail_parse(hundred_digits, "%100M", mi); // overflow
+        test_parse(seventy_zeroes + "55", "%100M", mi);
+        assert(mi == 55min);
+    }
+
+    {
+        seconds s{22s};
+        test_parse(hundred_digits, "%S", s);
+        assert(s == 11s);
+        test_parse(seventy_zeroes + "55", "%S", s);
+        assert(s == 0s);
+        fail_parse(hundred_digits, "%100S", s); // overflow
+        test_parse(seventy_zeroes + "55", "%100S", s);
+        assert(s == 55s);
+    }
+
+    {
+        weekday wd{Thursday};
+        test_parse(hundred_digits, "%u", wd);
+        assert(wd == Monday);
+        fail_parse(seventy_zeroes + "2", "%u", wd); // 0 is not a valid weekday for %u
+        fail_parse(hundred_digits, "%100u", wd); // overflow
+        test_parse(seventy_zeroes + "2", "%100u", wd);
+        assert(wd == Tuesday);
+
+        test_parse(hundred_digits, "%w", wd);
+        assert(wd == Monday);
+        test_parse(seventy_zeroes + "2", "%w", wd);
+        assert(wd == Sunday);
+        fail_parse(hundred_digits, "%100w", wd); // overflow
+        test_parse(seventy_zeroes + "2", "%100w", wd);
+        assert(wd == Tuesday);
+    }
+
+    {
+        year y{1970y};
+        test_parse(hundred_digits, "%y", y);
+        assert(y == 2011y);
+        test_parse(seventy_zeroes + "55", "%y", y);
+        assert(y == 2000y);
+        fail_parse(hundred_digits, "%100y", y); // overflow
+        test_parse(seventy_zeroes + "55", "%100y", y);
+        assert(y == 2055y);
+
+        test_parse(hundred_digits, "%Y", y);
+        assert(y == 1111y);
+        test_parse(seventy_zeroes + "2026", "%Y", y);
+        assert(y == 0y);
+        fail_parse(hundred_digits, "%100Y", y); // overflow
+        test_parse(seventy_zeroes + "2026", "%100Y", y);
+        assert(y == 2026y);
+
+        test_parse("33 " + hundred_digits, "%y %C", y);
+        assert(y == 1133y);
+        test_parse("33 " + seventy_zeroes + "22", "%y %C", y);
+        assert(y == 33y);
+        fail_parse("33 " + hundred_digits, "%y %100C", y); // overflow
+        test_parse("33 " + seventy_zeroes + "22", "%y %100C", y);
+        assert(y == 2233y);
+    }
+}
+
 template <class CharT, class CStringOrStdString>
 void test_io_manipulator() {
     seconds time;
@@ -1254,6 +1440,29 @@ void test_io_manipulator() {
     fail_parse(WIDEN(CharT, "a  b"), CStringOrStdString{WIDEN(CharT, "a%nb")}, time);
 }
 
+void test_lwg_3536() {
+    // LWG-3536, "Should chrono::from_stream() assign zero to duration for failure?"
+    minutes mm{20};
+
+    {
+        istringstream iss{"2:2:30"};
+        iss >> parse("%H:%M:%S", mm);
+        assert(iss.fail() && mm == 20min);
+    }
+
+    {
+        istringstream iss{"June"};
+        iss >> parse("%B", mm);
+        assert(iss.fail() && mm == 20min);
+    }
+
+    {
+        istringstream iss{""};
+        iss >> parse("%B", mm);
+        assert(iss.fail() && mm == 20min);
+    }
+}
+
 namespace lwg_3956 {
     struct has_adl_from_stream {
         int value = 0;
@@ -1297,9 +1506,7 @@ void test_lwg_3956() {
     }
 }
 
-void test_parse() {
-    test_lwg_3536();
-    test_lwg_3956();
+void test_all_parse() {
     parse_seconds();
     parse_minutes();
     parse_hours();
@@ -1311,15 +1518,18 @@ void test_parse() {
     parse_incomplete();
     parse_whitespace();
     parse_timepoints();
+    parse_modified_maximum_characters();
     test_io_manipulator<char, const char*>();
     test_io_manipulator<wchar_t, const wchar_t*>();
     test_io_manipulator<char, string>();
     test_io_manipulator<wchar_t, wstring>();
+    test_lwg_3536();
+    test_lwg_3956();
 }
 
 void test() {
     test_duration_output();
-    test_parse();
+    test_all_parse();
 }
 
 int main() {