diff --git a/stl/inc/regex b/stl/inc/regex
index b5fa6cae39..ea93da183d 100644
--- a/stl/inc/regex
+++ b/stl/inc/regex
@@ -149,7 +149,7 @@ namespace regex_constants {
         error_badrepeat,
         error_complexity,
         error_stack,
-        error_parse,
+        _Error_parse, // TRANSITION, was error_parse, keeping behavior
         error_syntax
     };
 } // namespace regex_constants
@@ -464,12 +464,12 @@ _EXPORT_STD class _NODISCARD regex_error : public runtime_error { // type of all
 public:
     explicit regex_error(regex_constants::error_type _Ex) : runtime_error(_Stringify(_Ex)), _Err(_Ex) {}
 
-    _NODISCARD regex_constants::error_type code() const {
+    _NODISCARD regex_constants::error_type code() const noexcept /* strengthened */ {
         return _Err;
     }
 
 private:
-    static const char* _Stringify(regex_constants::error_type _Ex) { // map error code to string
+    static const char* _Stringify(regex_constants::error_type _Ex) noexcept { // map error code to string
         switch (_Ex) { // select known error_type message
         case regex_constants::error_collate:
             return "regex_error(error_collate): The expression "
@@ -515,7 +515,7 @@ private:
             return "regex_error(error_stack): There was insufficient "
                    "memory to determine whether the regular expression "
                    "could match the specified character sequence.";
-        case regex_constants::error_parse:
+        case regex_constants::_Error_parse: // TRANSITION, keeping behavior
             return "regex_error(error_parse)";
         case regex_constants::error_syntax:
             return "regex_error(error_syntax)";
@@ -1820,12 +1820,10 @@ public:
     }
 
     basic_regex(_In_reads_(_Count) const _Elem* _Ptr, size_t _Count, flag_type _Flags = regex_constants::ECMAScript) {
-        if (_Ptr) {
-            _Reset(_Ptr, _Ptr + _Count, _Flags);
-            return;
-        }
-
-        _Xregex_error(regex_constants::error_parse);
+#if _ITERATOR_DEBUG_LEVEL != 0
+        _STL_VERIFY(_Ptr != nullptr || _Count == 0, "constructing basic_regex from an invalid range");
+#endif // ^^^ _ITERATOR_DEBUG_LEVEL != 0 ^^^
+        _Reset(_Ptr, _Ptr + _Count, _Flags);
     }
 
     template <class _STtraits, class _STalloc>
@@ -3652,7 +3650,11 @@ bool _Matcher<_BidIt, _Elem, _RxTraits, _It>::_Match_pat(_Node_base* _Nx) { // c
 
         case _N_none:
         default:
-            _Xregex_error(regex_constants::error_parse);
+#if _ITERATOR_DEBUG_LEVEL != 0
+            _STL_VERIFY(false, "internal data of regex node corrupted");
+#else // ^^^ _ITERATOR_DEBUG_LEVEL != 0 / _ITERATOR_DEBUG_LEVEL == 0 vvv
+            return false;
+#endif // ^^^ _ITERATOR_DEBUG_LEVEL == 0 ^^^
         }
 
         if (_Failed) {
diff --git a/tests/std/tests/GH_002206_unreserved_names/test.compile.pass.cpp b/tests/std/tests/GH_002206_unreserved_names/test.compile.pass.cpp
index 8ba419dbd0..302200fc3e 100644
--- a/tests/std/tests/GH_002206_unreserved_names/test.compile.pass.cpp
+++ b/tests/std/tests/GH_002206_unreserved_names/test.compile.pass.cpp
@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #define ISA_AVAILABILITY delete
+#define error_parse      delete
 #define nsec             delete
 #define sec              delete
 #define xtime            delete
diff --git a/tests/std/tests/VSO_0000000_regex_use/test.cpp b/tests/std/tests/VSO_0000000_regex_use/test.cpp
index ad2efc0d4a..0eea2f88ad 100644
--- a/tests/std/tests/VSO_0000000_regex_use/test.cpp
+++ b/tests/std/tests/VSO_0000000_regex_use/test.cpp
@@ -547,6 +547,17 @@ void test_VSO_226914_word_boundaries() {
     aWordAny.should_search_fail("aa", match_not_bow | match_not_eow);
 }
 
+void test_construction_from_nullptr_and_zero() {
+    {
+        regex re(nullptr, 0);
+        assert(re.mark_count() == 0);
+    }
+    {
+        wregex re(nullptr, 0);
+        assert(re.mark_count() == 0);
+    }
+}
+
 void test_gh_993() {
     // GH-993 regex::icase is not handled correctly for some input.
     {
@@ -695,6 +706,7 @@ int main() {
     test_VSO_225160_match_bol_flag();
     test_VSO_225160_match_eol_flag();
     test_VSO_226914_word_boundaries();
+    test_construction_from_nullptr_and_zero();
     test_gh_993();
     test_gh_4995();
     test_gh_5058();