diff --git a/ext/calendar/calendar.c b/ext/calendar/calendar.c
index f26d611092db..bca065549e5c 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 month, zend_long day, zend_long year);
 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..2e20698e4d96 100644
--- a/ext/calendar/jewish.c
+++ b/ext/calendar/jewish.c
@@ -531,13 +531,17 @@ static void FindTishriMolad(
  * and time of the starting molad.
  */
 static void FindStartOfYear(
-							   int year,
+							   zend_long year,
 							   int *pMetonicCycle,
 							   int *pMetonicYear,
 							   zend_long *pMoladDay,
 							   zend_long *pMoladHalakim,
 							   int *pTishri1)
 {
+	/* JewishToSdn() rejects years outside this range, so the int outputs
+	 * below cannot overflow. */
+	ZEND_ASSERT(year > 0 && year < INT_MAX);
+
 	*pMetonicCycle = (year - 1) / 19;
 	*pMetonicYear = (year - 1) % 19;
 	MoladOfMetonicCycle(*pMetonicCycle, pMoladDay, pMoladHalakim);
@@ -696,9 +700,9 @@ 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;
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..ed03c4452940 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 accepted year: the resulting day count no longer fits in an int. */
+echo juliantojd(5, 5, 2147478847) . "\n";
+/* Beyond that the date is out of range for the Julian calendar. */
 echo juliantojd(5, 5, 6000000000) . "\n";
 ?>
 --EXPECT--
-622764916319
+784368370049
+0
diff --git a/ext/calendar/tests/tojd_narrowing.phpt b/ext/calendar/tests/tojd_narrowing.phpt
new file mode 100644
index 000000000000..bc82c1a50d1e
--- /dev/null
+++ b/ext/calendar/tests/tojd_narrowing.phpt
@@ -0,0 +1,44 @@
+--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, ': ', $e->getMessage(), "\n";
+    }
+}
+?>
+--EXPECT--
+gregoriantojd
+int(1721426)
+int(0)
+int(0)
+int(0)
+juliantojd
+int(1721424)
+int(0)
+int(0)
+int(0)
+jewishtojd
+int(347998)
+int(0)
+int(0)
+ValueError: jewishtojd(): Argument #3 ($year) must be between -2147483648 and 2147483647
+frenchtojd
+int(2375840)
+int(0)
+int(0)
+int(0)