diff --git a/NEWS b/NEWS
index 7c9c4f08ed1b..bacb68f387d0 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,10 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? ????, PHP 8.6.0RC1
 
+- Core:
+  . Fixed incorrect internal pointer and foreach iterator positions when
+    compacting arrays with holes. (Weilin Du)
+
 - DOM:
   . Fixed use-after-free when re-constructing a DOMXPath whose php:function
     registrations are freed while still reachable from the cycle collector.
@@ -26,6 +30,10 @@ PHP                                                                        NEWS
   . Fixed bug GH-23242 (PHP development server does not support Expect
     100-continue flow control). (Sjoerd Langkemper)
 
+- Calendar:
+  . Fixed *tojd() functions and cal_to_jd() truncating arguments outside the
+    int range instead of rejecting them. (lacatoire)
+
 - DOM:
   . Fixed NamedNodeMap::getNamedItemNS() with an empty URI not matching
     the null namespace in spec-following mode. (Ilia Alshanetsky)
diff --git a/Zend/tests/array_dup_internal_pointer_hole.phpt b/Zend/tests/array_dup_internal_pointer_hole.phpt
new file mode 100644
index 000000000000..97fdd40bb1ad
--- /dev/null
+++ b/Zend/tests/array_dup_internal_pointer_hole.phpt
@@ -0,0 +1,45 @@
+--TEST--
+Array duplication relocates an internal pointer on a hole, with and without foreach iterators
+--FILE--
+<?php
+function duplicate(array &$values): void {
+    $copy = $values;
+    $values['i'] = 18;
+    echo 'current: ', key($values), '=>', current($values), "\n";
+    next($values);
+    echo 'next: ', key($values), '=>', current($values), "\n";
+    echo 'copy current: ', key($copy), '=>', current($copy), "\n";
+    echo 'copy keys: ', implode(' ', array_keys($copy)), "\n";
+}
+
+foreach ([false, true] as $withIterator) {
+    echo $withIterator ? "With iterator:\n" : "Without iterator:\n";
+    $values = ['a' => 10, 'b' => 11, 'c' => 12, 'd' => 13,
+               'e' => 14, 'f' => 15, 'g' => 16, 'h' => 17];
+    next($values);
+    next($values);
+    // Leave the internal pointer on a hole before several surviving elements.
+    unset($values['a'], $values['b'], $values['c'], $values['d']);
+
+    if ($withIterator) {
+        foreach ($values as &$value) {
+            duplicate($values);
+            break;
+        }
+        unset($value);
+    } else {
+        duplicate($values);
+    }
+}
+?>
+--EXPECT--
+Without iterator:
+current: e=>14
+next: f=>15
+copy current: e=>14
+copy keys: e f g h
+With iterator:
+current: e=>14
+next: f=>15
+copy current: e=>14
+copy keys: e f g h
diff --git a/Zend/tests/array_dup_iterator_past_end.phpt b/Zend/tests/array_dup_iterator_past_end.phpt
new file mode 100644
index 000000000000..80e52e3e5ab2
--- /dev/null
+++ b/Zend/tests/array_dup_iterator_past_end.phpt
@@ -0,0 +1,23 @@
+--TEST--
+Array duplication preserves past-the-end iterators when compacting holes
+--FILE--
+<?php
+$values = ['a' => 10, 'b' => 11, 'c' => 12, 'd' => 13];
+unset($values['a'], $values['b']);
+
+foreach ($values as $key => &$value) {
+    echo "$key=>$value\n";
+    if ($key === 'd') {
+        // The iterator is one past the end; COW compacts the preceding holes.
+        $copy = $values;
+        $values['e'] = 14;
+    }
+}
+unset($value);
+echo 'copy: ', implode(' ', array_keys($copy)), "\n";
+?>
+--EXPECT--
+c=>12
+d=>13
+e=>14
+copy: c d
diff --git a/Zend/tests/array_dup_multiple_iterators.phpt b/Zend/tests/array_dup_multiple_iterators.phpt
new file mode 100644
index 000000000000..96f2dbb7f8de
--- /dev/null
+++ b/Zend/tests/array_dup_multiple_iterators.phpt
@@ -0,0 +1,38 @@
+--TEST--
+Array duplication updates iterators at both a hole and the next defined element
+--FILE--
+<?php
+function test(array $values): void {
+    $outerVisits = [];
+    $innerVisits = [];
+    $first = true;
+    foreach ($values as $outerKey => &$outerValue) {
+        $outerVisits[] = "$outerKey=>$outerValue";
+        if ($first) {
+            $first = false;
+            foreach ($values as $innerKey => &$innerValue) {
+                $innerVisits[] = "$innerKey=>$innerValue";
+                if ($innerValue === 11) {
+                    // The outer cursor is at a hole, the inner at the next value.
+                    unset($values['a'], $values['b']);
+                    $copy = $values;
+                    // Trigger copy-on-write duplication, which compacts the holes.
+                    $values['i'] = 18;
+                }
+            }
+            unset($innerValue);
+        }
+    }
+    unset($outerValue);
+    echo 'outer: ', implode(' ', $outerVisits), "\n";
+    echo 'inner: ', implode(' ', $innerVisits), "\n";
+    echo 'copy: ', implode(' ', array_keys($copy)), "\n";
+}
+
+test(['a' => 10, 'b' => 11, 'c' => 12, 'd' => 13,
+      'e' => 14, 'f' => 15, 'g' => 16, 'h' => 17]);
+?>
+--EXPECT--
+outer: a=>10 c=>12 d=>13 e=>14 f=>15 g=>16 h=>17 i=>18
+inner: a=>10 b=>11 c=>12 d=>13 e=>14 f=>15 g=>16 h=>17 i=>18
+copy: c d e f g h
diff --git a/Zend/tests/deprecated_identifiers/underscore/class_alias_underscore.phpt b/Zend/tests/deprecated_identifiers/underscore/class_alias_underscore.phpt
new file mode 100644
index 000000000000..23afcbfeb92e
--- /dev/null
+++ b/Zend/tests/deprecated_identifiers/underscore/class_alias_underscore.phpt
@@ -0,0 +1,14 @@
+--TEST--
+Using "_" as a class name alias is deprecated
+--FILE--
+<?php
+
+class_alias('stdClass', '_');
+
+class_alias('stdClass', 'Foo\\_');
+
+?>
+--EXPECTF--
+Deprecated: Using "_" as a class alias is deprecated since 8.4 in %s on line %d
+
+Deprecated: Using "_" as a class alias is deprecated since 8.4 in %s on line %d
diff --git a/Zend/tests/class_underscore_as_name.phpt b/Zend/tests/deprecated_identifiers/underscore/class_underscore_as_name.phpt
similarity index 100%
rename from Zend/tests/class_underscore_as_name.phpt
rename to Zend/tests/deprecated_identifiers/underscore/class_underscore_as_name.phpt
diff --git a/Zend/tests/deprecated_identifiers/underscore/class_underscore_as_name_use.phpt b/Zend/tests/deprecated_identifiers/underscore/class_underscore_as_name_use.phpt
new file mode 100644
index 000000000000..685250b369ac
--- /dev/null
+++ b/Zend/tests/deprecated_identifiers/underscore/class_underscore_as_name_use.phpt
@@ -0,0 +1,18 @@
+--TEST--
+Using "_" as a class name in use statements is deprecated
+--FILE--
+<?php
+
+namespace Foo\Bar {
+    use stdClass as _;
+}
+
+namespace {
+    use stdClass as _;
+}
+
+?>
+--EXPECTF--
+Deprecated: Using "_" as a class name is deprecated in %s on line %d
+
+Deprecated: Using "_" as a class name is deprecated in %s on line %d
diff --git a/Zend/tests/deprecated_identifiers/underscore/constant_underscore_as_name.phpt b/Zend/tests/deprecated_identifiers/underscore/constant_underscore_as_name.phpt
new file mode 100644
index 000000000000..4859e8ca5aeb
--- /dev/null
+++ b/Zend/tests/deprecated_identifiers/underscore/constant_underscore_as_name.phpt
@@ -0,0 +1,28 @@
+--TEST--
+Using "_" as a constant name is deprecated
+--FILE--
+<?php
+
+namespace Foo\Bar {
+    const _ = 5;
+}
+
+namespace {
+    const _ = 5;
+
+    define('_', 'x');
+
+    define('foo\\_', 'x');
+}
+
+?>
+--EXPECTF--
+Deprecated: Calling a constant "_" is deprecated since 8.6 in %s on line %d
+
+Deprecated: Calling a constant "_" is deprecated since 8.6 in %s on line %d
+
+Deprecated: Calling a constant "_" is deprecated since 8.6 in %s on line %d
+
+Warning: Constant _ already defined, this will be an error in PHP 9 in %s on line %d
+
+Deprecated: Calling a constant "_" is deprecated since 8.6 in %s on line %d
diff --git a/Zend/tests/deprecated_identifiers/underscore/constant_underscore_as_name_use.phpt b/Zend/tests/deprecated_identifiers/underscore/constant_underscore_as_name_use.phpt
new file mode 100644
index 000000000000..e7421318aead
--- /dev/null
+++ b/Zend/tests/deprecated_identifiers/underscore/constant_underscore_as_name_use.phpt
@@ -0,0 +1,18 @@
+--TEST--
+Using "_" as a constant in use statements is deprecated
+--FILE--
+<?php
+
+namespace Foo\Bar {
+    use const PHP_INT_MAX as _;
+}
+
+namespace {
+    use const PHP_INT_MAX as _;
+}
+
+?>
+--EXPECTF--
+Deprecated: Using "_" as a constant name is deprecated since 8.6 in %s on line %d
+
+Deprecated: Using "_" as a constant name is deprecated since 8.6 in %s on line %d
diff --git a/Zend/tests/deprecated_identifiers/underscore/function_underscore_as_name.phpt b/Zend/tests/deprecated_identifiers/underscore/function_underscore_as_name.phpt
new file mode 100644
index 000000000000..0d127fab6300
--- /dev/null
+++ b/Zend/tests/deprecated_identifiers/underscore/function_underscore_as_name.phpt
@@ -0,0 +1,23 @@
+--TEST--
+Using "_" as a function name is NOT deprecated
+--SKIPIF--
+<?php
+if (extension_loaded('gettext')) {
+    die("skip gettext extension defines the _ function");
+}
+?>
+--FILE--
+<?php
+
+namespace Foo\Bar {
+    function _() {}
+}
+
+namespace {
+    function _() {}
+    echo "OK";
+}
+
+?>
+--EXPECT--
+OK
diff --git a/Zend/tests/deprecated_identifiers/underscore/function_underscore_as_name_use.phpt b/Zend/tests/deprecated_identifiers/underscore/function_underscore_as_name_use.phpt
new file mode 100644
index 000000000000..688683a60396
--- /dev/null
+++ b/Zend/tests/deprecated_identifiers/underscore/function_underscore_as_name_use.phpt
@@ -0,0 +1,18 @@
+--TEST--
+Using "_" as a function in use statements is NOT deprecated
+--FILE--
+<?php
+
+namespace Foo\Bar {
+    use function strlen as _;
+}
+
+namespace {
+    use function strlen as _;
+
+    echo "OK";
+}
+
+?>
+--EXPECT--
+OK
diff --git a/Zend/tests/rehash_multiple_iterators.phpt b/Zend/tests/rehash_multiple_iterators.phpt
new file mode 100644
index 000000000000..cbbfc75d703a
--- /dev/null
+++ b/Zend/tests/rehash_multiple_iterators.phpt
@@ -0,0 +1,40 @@
+--TEST--
+Rehashing updates iterators at both a hole and the next defined element
+--FILE--
+<?php
+function test(array $values, $firstKey, $secondKey, $newKey, int $newValue): void {
+    $outerVisits = [];
+    $innerVisits = [];
+    $first = true;
+    foreach ($values as $outerKey => &$outerValue) {
+        $outerVisits[] = "$outerKey=>$outerValue";
+        if ($first) {
+            $first = false;
+            foreach ($values as $innerKey => &$innerValue) {
+                $innerVisits[] = "$innerKey=>$innerValue";
+                if ($innerValue === 11) {
+                    // The outer cursor is at a hole, the inner at the next value.
+                    unset($values[$firstKey], $values[$secondKey]);
+                    $values[$newKey] = $newValue;
+                }
+            }
+            unset($innerValue);
+        }
+    }
+    unset($outerValue);
+    echo 'outer: ', implode(' ', $outerVisits), "\n";
+    echo 'inner: ', implode(' ', $innerVisits), "\n";
+}
+
+// Adding a string key converts packed storage and compacts its holes.
+test([10, 11, 12, 13, 14], 0, 1, 'new', 15);
+
+// Inserting into a full mixed table compacts its holes without growing it.
+test(['a' => 10, 'b' => 11, 'c' => 12, 'd' => 13,
+      'e' => 14, 'f' => 15, 'g' => 16, 'h' => 17], 'a', 'b', 'i', 18);
+?>
+--EXPECT--
+outer: 0=>10 2=>12 3=>13 4=>14 new=>15
+inner: 0=>10 1=>11 2=>12 3=>13 4=>14 new=>15
+outer: a=>10 c=>12 d=>13 e=>14 f=>15 g=>16 h=>17 i=>18
+inner: a=>10 b=>11 c=>12 d=>13 e=>14 f=>15 g=>16 h=>17 i=>18
diff --git a/Zend/zend_compile.c b/Zend/zend_compile.c
index 317114265c57..5aa1b07f304d 100644
--- a/Zend/zend_compile.c
+++ b/Zend/zend_compile.c
@@ -252,7 +252,7 @@ void zend_assert_valid_class_name(const zend_string *name, const char *type) /*
 		zend_error_noreturn(E_COMPILE_ERROR,
 			"Cannot use \"%s\" as %s as it is reserved", ZSTR_VAL(name), type);
 	}
-	if (zend_string_equals_literal(name, "_")) {
+	if (zend_string_equals_literal(name, "_") || zend_string_ends_with_literal(name, "\\_")) {
 		zend_error(E_DEPRECATED, "Using \"_\" as %s is deprecated since 8.4", type);
 	}
 }
@@ -10213,6 +10213,20 @@ static void zend_compile_use(zend_ast *ast) /* {{{ */
 				"is a special class name", ZSTR_VAL(old_name), ZSTR_VAL(new_name), ZSTR_VAL(new_name));
 		}
 
+		if (zend_string_equals(new_name, ZSTR_CHAR('_'))) {
+			switch (type) {
+				case ZEND_SYMBOL_CLASS:
+					zend_error(E_DEPRECATED, "Using \"_\" as a class name is deprecated");
+					break;
+				case ZEND_SYMBOL_CONST:
+					zend_error(E_DEPRECATED, "Using \"_\" as a constant name is deprecated since 8.6");
+					break;
+				case ZEND_SYMBOL_FUNCTION:
+					break;
+				default: ZEND_UNREACHABLE();
+			}
+		}
+
 		if (current_ns) {
 			zend_string *ns_name = zend_string_alloc(ZSTR_LEN(current_ns) + 1 + ZSTR_LEN(new_name), 0);
 			zend_str_tolower_copy(ZSTR_VAL(ns_name), ZSTR_VAL(current_ns), ZSTR_LEN(current_ns));
diff --git a/Zend/zend_constants.c b/Zend/zend_constants.c
index 18292203bee9..c8a2ae62d756 100644
--- a/Zend/zend_constants.c
+++ b/Zend/zend_constants.c
@@ -538,6 +538,12 @@ ZEND_API zend_constant *zend_register_constant(zend_constant *c)
 
 	c->attributes = NULL;
 
+	if (
+		zend_string_equals(name, ZSTR_CHAR('_'))
+		|| (slash && zend_string_ends_with_literal(name, "\\_"))
+	) {
+		zend_error(E_DEPRECATED, "Calling a constant \"_\" is deprecated since 8.6");
+	}
 	/* Check if the user is trying to define any special constant */
 	if (zend_string_equals_literal(name, "__COMPILER_HALT_OFFSET__")
 		|| (!persistent && zend_get_special_const(ZSTR_VAL(name), ZSTR_LEN(name)))
diff --git a/Zend/zend_hash.c b/Zend/zend_hash.c
index 84751a02e7c0..4640846ecc76 100644
--- a/Zend/zend_hash.c
+++ b/Zend/zend_hash.c
@@ -1420,7 +1420,7 @@ ZEND_API void ZEND_FASTCALL zend_hash_rehash(HashTable *ht)
 								do {
 									zend_hash_iterators_update(ht, iter_pos, j);
 									iter_pos = zend_hash_iterators_lower_pos(ht, iter_pos + 1);
-								} while (iter_pos < i);
+								} while (iter_pos <= i);
 							}
 							q++;
 							j++;
@@ -2416,7 +2416,7 @@ static zend_always_inline uint32_t zend_array_dup_elements(const HashTable *sour
 			if (EXPECTED(!HT_HAS_ITERATORS(target))) {
 				while (p != end) {
 					if (zend_array_dup_element(source, target, target_idx, p, q, false, static_keys, with_holes)) {
-						if (source->nInternalPointer == idx) {
+						if (UNEXPECTED(target->nInternalPointer > target_idx && target->nInternalPointer <= idx)) {
 							target->nInternalPointer = target_idx;
 						}
 						target_idx++; q++;
@@ -2429,19 +2429,21 @@ static zend_always_inline uint32_t zend_array_dup_elements(const HashTable *sour
 
 				while (p != end) {
 					if (zend_array_dup_element(source, target, target_idx, p, q, false, static_keys, with_holes)) {
-						if (source->nInternalPointer == idx) {
+						if (UNEXPECTED(target->nInternalPointer > target_idx && target->nInternalPointer <= idx)) {
 							target->nInternalPointer = target_idx;
 						}
 						if (UNEXPECTED(idx >= iter_pos)) {
 							do {
 								zend_hash_iterators_update(target, iter_pos, target_idx);
 								iter_pos = zend_hash_iterators_lower_pos(target, iter_pos + 1);
-							} while (iter_pos < idx);
+							} while (iter_pos <= idx);
 						}
 						target_idx++; q++;
 					}
 					idx++; p++;
 				}
+				/* Move past-the-end iterators so they can pick up newly appended elements. */
+				_zend_hash_iterators_update(target, source->nNumUsed, target_idx);
 			}
 			return target_idx;
 		}
diff --git a/ext/calendar/calendar.c b/ext/calendar/calendar.c
index f26d611092db..14daf3a5e678 100644
--- a/ext/calendar/calendar.c
+++ b/ext/calendar/calendar.c
@@ -41,7 +41,7 @@ enum cal_name_type_t {
 	CAL_NUM_CALS
 };
 
-typedef zend_long (*cal_to_jd_func_t) (int month, int day, int year);
+typedef zend_long (*cal_to_jd_func_t) (zend_long year, zend_long month, zend_long day);
 typedef void (*cal_from_jd_func_t) (zend_long jd, int *year, int *month, int *day);
 typedef char *(*cal_as_string_func_t) (int year, int month, int day);
 
diff --git a/ext/calendar/french.c b/ext/calendar/french.c
index 0707e27ed8d1..913098325629 100644
--- a/ext/calendar/french.c
+++ b/ext/calendar/french.c
@@ -115,9 +115,9 @@ void SdnToFrench(
 }
 
 zend_long FrenchToSdn(
-						int year,
-						int month,
-						int day)
+						zend_long year,
+						zend_long month,
+						zend_long day)
 {
 	/* check for invalid dates */
 	if (year < 1 || year > 14 ||
diff --git a/ext/calendar/gregor.c b/ext/calendar/gregor.c
index eaee9c8c73c7..4047051cf3e1 100644
--- a/ext/calendar/gregor.c
+++ b/ext/calendar/gregor.c
@@ -200,12 +200,12 @@ void SdnToGregorian(
 }
 
 zend_long GregorianToSdn(
-						   int inputYear,
-						   int inputMonth,
-						   int inputDay)
+						   zend_long inputYear,
+						   zend_long inputMonth,
+						   zend_long inputDay)
 {
 	zend_long year;
-	int month;
+	zend_long month;
 
 	/* check for invalid dates */
 	if (inputYear == 0 || inputYear < -4714 ||
diff --git a/ext/calendar/jewish.c b/ext/calendar/jewish.c
index b589c4cb2617..c6aec67c8548 100644
--- a/ext/calendar/jewish.c
+++ b/ext/calendar/jewish.c
@@ -696,9 +696,9 @@ void SdnToJewish(
  * and compare with the original.
  */
 zend_long JewishToSdn(
-						int year,
-						int month,
-						int day)
+						zend_long year,
+						zend_long month,
+						zend_long day)
 {
 	zend_long sdn;
 	int metonicCycle;
@@ -713,11 +713,14 @@ zend_long JewishToSdn(
 	if (year <= 0 || year >= INT_MAX - 1 || day <= 0 || day > 30) {
 		return (0);
 	}
+	/* The check above leaves both year and year + 1 within int range. */
+	int int_year = (int) year;
+
 	switch (month) {
 		case 1:
 		case 2:
 			/* It is Tishri or Heshvan - don't need the year length. */
-			FindStartOfYear(year, &metonicCycle, &metonicYear,
+			FindStartOfYear(int_year, &metonicCycle, &metonicYear,
 							&moladDay, &moladHalakim, &tishri1);
 			if (month == 1) {
 				sdn = tishri1 + day - 1;
@@ -730,7 +733,7 @@ zend_long JewishToSdn(
 			/* It is Kislev - must find the year length. */
 
 			/* Find the start of the year. */
-			FindStartOfYear(year, &metonicCycle, &metonicYear,
+			FindStartOfYear(int_year, &metonicCycle, &metonicYear,
 							&moladDay, &moladHalakim, &tishri1);
 
 			/* Find the end of the year. */
@@ -753,10 +756,10 @@ zend_long JewishToSdn(
 		case 6:
 			/* It is Tevet, Shevat or Adar I - don't need the year length. */
 
-			FindStartOfYear(year + 1, &metonicCycle, &metonicYear,
+			FindStartOfYear(int_year + 1, &metonicCycle, &metonicYear,
 							&moladDay, &moladHalakim, &tishri1After);
 
-			if (monthsPerYear[(year - 1) % 19] == 12) {
+			if (monthsPerYear[(int_year - 1) % 19] == 12) {
 				lengthOfAdarIAndII = 29;
 			} else {
 				lengthOfAdarIAndII = 59;
@@ -773,7 +776,7 @@ zend_long JewishToSdn(
 
 		default:
 			/* It is Adar II or later - don't need the year length. */
-			FindStartOfYear(year + 1, &metonicCycle, &metonicYear,
+			FindStartOfYear(int_year + 1, &metonicCycle, &metonicYear,
 							&moladDay, &moladHalakim, &tishri1After);
 
 			switch (month) {
diff --git a/ext/calendar/julian.c b/ext/calendar/julian.c
index c24527941d3e..d539e2b45bd8 100644
--- a/ext/calendar/julian.c
+++ b/ext/calendar/julian.c
@@ -213,12 +213,12 @@ void SdnToJulian(
 }
 
 zend_long JulianToSdn(
-						int inputYear,
-						int inputMonth,
-						int inputDay)
+						zend_long inputYear,
+						zend_long inputMonth,
+						zend_long inputDay)
 {
 	zend_long year;
-	int month;
+	zend_long month;
 
 	/* check for invalid dates */
 	if (inputYear == 0 || inputYear < -4713 ||
diff --git a/ext/calendar/sdncal.h b/ext/calendar/sdncal.h
index fa3aa7c641a9..17202791c439 100644
--- a/ext/calendar/sdncal.h
+++ b/ext/calendar/sdncal.h
@@ -69,17 +69,17 @@
 
 /* Gregorian calendar conversions. */
 void SdnToGregorian(zend_long sdn, int *pYear, int *pMonth, int *pDay);
-zend_long GregorianToSdn(int year, int month, int day);
+zend_long GregorianToSdn(zend_long year, zend_long month, zend_long day);
 extern const char * const MonthNameShort[13];
 extern const char * const MonthNameLong[13];
 
 /* Julian calendar conversions. */
 void SdnToJulian(zend_long sdn, int *pYear, int *pMonth, int *pDay);
-zend_long JulianToSdn(int year, int month, int day);
+zend_long JulianToSdn(zend_long year, zend_long month, zend_long day);
 
 /* Jewish calendar conversions. */
 void SdnToJewish(zend_long sdn, int *pYear, int *pMonth, int *pDay);
-zend_long JewishToSdn(int year, int month, int day);
+zend_long JewishToSdn(zend_long year, zend_long month, zend_long day);
 extern const char * const JewishMonthName[14];
 extern const char * const JewishMonthNameLeap[14];
 extern const char * const JewishMonthHebName[14];
@@ -88,7 +88,7 @@ extern const int monthsPerYear[19];
 
 /* French republic calendar conversions. */
 void SdnToFrench(zend_long sdn, int *pYear, int *pMonth, int *pDay);
-zend_long FrenchToSdn(int inputYear, int inputMonth, int inputDay);
+zend_long FrenchToSdn(zend_long inputYear, zend_long inputMonth, zend_long inputDay);
 extern const char * const FrenchMonthName[14];
 
 /* Islamic calendar conversions. */
diff --git a/ext/calendar/tests/juliantojd_overflow.phpt b/ext/calendar/tests/juliantojd_overflow.phpt
index cdf1b203d96c..3422c6c7268d 100644
--- a/ext/calendar/tests/juliantojd_overflow.phpt
+++ b/ext/calendar/tests/juliantojd_overflow.phpt
@@ -6,7 +6,11 @@ calendar
 <?php if (PHP_INT_SIZE != 8) die("skip this test is for 64bit platform only"); ?>
 --FILE--
 <?php
+/* The largest year JulianToSdn() accepts, INT_MAX - 4800. */
+echo juliantojd(5, 5, 2147478847) . "\n";
+/* Anything above it is rejected rather than truncated. */
 echo juliantojd(5, 5, 6000000000) . "\n";
 ?>
 --EXPECT--
-622764916319
+784368370049
+0
diff --git a/ext/calendar/tests/tojd_out_of_int_range.phpt b/ext/calendar/tests/tojd_out_of_int_range.phpt
new file mode 100644
index 000000000000..aeb6b9c4b5c8
--- /dev/null
+++ b/ext/calendar/tests/tojd_out_of_int_range.phpt
@@ -0,0 +1,57 @@
+--TEST--
+*tojd(): arguments outside the int range must not alias into the accepted range
+--EXTENSIONS--
+calendar
+--SKIPIF--
+<?php if (PHP_INT_SIZE != 8) die("skip this test is for 64bit platform only"); ?>
+--FILE--
+<?php
+// Values whose low 32 bits land in the accepted range must still be rejected.
+$bias = 2 ** 32;
+
+foreach (['gregoriantojd', 'juliantojd', 'jewishtojd', 'frenchtojd'] as $function) {
+    echo $function, "\n";
+    var_dump($function(1, 1, 1));
+    var_dump($function(1 + $bias, 1, 1));
+    var_dump($function(1, 1 + $bias, 1));
+    try {
+        var_dump($function(1, 1, 1 + $bias));
+    } catch (Throwable $e) {
+        echo $e::class, ': ', $e->getMessage(), "\n";
+    }
+}
+
+// cal_to_jd() and cal_days_in_month() reach the same helpers through
+// cal_to_jd_func_t, and have no lower bound on $year of their own.
+echo "cal_to_jd\n";
+var_dump(cal_to_jd(CAL_GREGORIAN, 1, 1, 1 - $bias));
+try {
+    var_dump(cal_days_in_month(CAL_GREGORIAN, 1, 1 - $bias));
+} catch (Throwable $e) {
+    echo $e::class, ': ', $e->getMessage(), "\n";
+}
+?>
+--EXPECT--
+gregoriantojd
+int(1721426)
+int(0)
+int(0)
+int(0)
+juliantojd
+int(1721424)
+int(0)
+int(0)
+int(0)
+jewishtojd
+int(347998)
+int(0)
+int(0)
+ValueError: jewishtojd(): Argument #3 ($year) must be between -2147483648 and 2147483647
+frenchtojd
+int(2375840)
+int(0)
+int(0)
+int(0)
+cal_to_jd
+int(0)
+ValueError: Invalid date