diff --git a/ext/calendar/calendar.c b/ext/calendar/calendar.c
index 54f2658eeae..6eb2d31beff 100644
--- a/ext/calendar/calendar.c
+++ b/ext/calendar/calendar.c
@@ -348,8 +348,15 @@ PHP_FUNCTION(cal_days_in_month)
 	sdn_next = calendar->to_jd(year, 1 + month, 1);
 
 	if (sdn_next == 0) {
-/* if invalid, try first month of the next year... */
-		sdn_next = calendar->to_jd(year + 1, 1, 1);
+		/* If the next month is invalid, then we need to try the first month of
+		 * the next year, bearing in mind that the next year after 1 BCE is
+		 * actually 1 AD and not 0. */
+		if (year == -1) {
+			sdn_next = calendar->to_jd(1, 1, 1);
+		}
+		else {
+			sdn_next = calendar->to_jd(year + 1, 1, 1);
+		}
 	}
 
 	RETURN_LONG(sdn_next - sdn_start);
diff --git a/ext/calendar/tests/bug52744.phpt b/ext/calendar/tests/bug52744.phpt
new file mode 100644
index 00000000000..886086a294d
--- /dev/null
+++ b/ext/calendar/tests/bug52744.phpt
@@ -0,0 +1,12 @@
+--TEST--
+Bug #52744 (cal_days_in_month incorrect for December 1 BCE)
+--SKIPIF--
+<?php include 'skipif.inc'; ?>
+--FILE--
+<?php
+var_dump(cal_days_in_month(CAL_GREGORIAN, 12, -1));
+var_dump(cal_days_in_month(CAL_JULIAN, 12, -1));
+?>
+--EXPECT--
+int(31)
+int(31)