diff --git a/src/Model/Serializer/ValueObject/Calendar/CalendarSerializer.php b/src/Model/Serializer/ValueObject/Calendar/CalendarSerializer.php
index 868fd47da..f7e542592 100644
--- a/src/Model/Serializer/ValueObject/Calendar/CalendarSerializer.php
+++ b/src/Model/Serializer/ValueObject/Calendar/CalendarSerializer.php
@@ -87,6 +87,15 @@ function ($openingHourData) {
             );
         }
 
+        // There are cases where the calendar type does not match the number of sub events.
+        // For those cases the amount of sub events dictates the calendar type.
+        if ($calendarType->sameAs(CalendarType::single()) && count($subEvents) > 1) {
+            $calendarType = CalendarType::multiple();
+        }
+        if ($calendarType->sameAs(CalendarType::multiple()) && count($subEvents) === 1) {
+            $calendarType = CalendarType::single();
+        }
+
         switch ($calendarType) {
             case CalendarType::single():
                 $calendar = new SingleSubEventCalendar($subEvents[0]);
diff --git a/tests/Model/Serializer/ValueObject/Calendar/CalendarSerializerTest.php b/tests/Model/Serializer/ValueObject/Calendar/CalendarSerializerTest.php
new file mode 100644
index 000000000..8de25e5a9
--- /dev/null
+++ b/tests/Model/Serializer/ValueObject/Calendar/CalendarSerializerTest.php
@@ -0,0 +1,237 @@
+<?php
+
+declare(strict_types=1);
+
+namespace CultuurNet\UDB3\Model\Serializer\ValueObject\Calendar;
+
+use CultuurNet\UDB3\Model\ValueObject\Calendar\BookingAvailability;
+use CultuurNet\UDB3\Model\ValueObject\Calendar\DateRange;
+use CultuurNet\UDB3\Model\ValueObject\Calendar\MultipleSubEventsCalendar;
+use CultuurNet\UDB3\Model\ValueObject\Calendar\SingleSubEventCalendar;
+use CultuurNet\UDB3\Model\ValueObject\Calendar\Status;
+use CultuurNet\UDB3\Model\ValueObject\Calendar\StatusType;
+use CultuurNet\UDB3\Model\ValueObject\Calendar\SubEvent;
+use CultuurNet\UDB3\Model\ValueObject\Calendar\SubEvents;
+use DateTimeImmutable;
+use PHPUnit\Framework\TestCase;
+
+final class CalendarSerializerTest extends TestCase
+{
+    /**
+     * @test
+     */
+    public function it_can_serialize_a_calendar(): void
+    {
+        $calendar = new SingleSubEventCalendar(
+            new SubEvent(
+                new DateRange(
+                    new DateTimeImmutable('2021-01-01T00:00:00+01:00'),
+                    new DateTimeImmutable('2021-01-02T00:00:00+01:00')
+                ),
+                new Status(StatusType::Available()),
+                BookingAvailability::Available()
+            )
+        );
+
+        $serializer = new CalendarSerializer($calendar);
+
+        $this->assertEquals(
+            [
+                'type' => 'single',
+                'status' => [
+                    'type' => 'Available',
+                ],
+                'bookingAvailability' => [
+                    'type' => 'Available',
+                ],
+                'timestamps' => [
+                    0 => [
+                        'startDate' => '2021-01-01T00:00:00+01:00',
+                        'endDate' => '2021-01-02T00:00:00+01:00',
+                        'status' => [
+                            'type' => 'Available',
+                        ],
+                        'bookingAvailability' => [
+                            'type' => 'Available',
+                        ],
+                    ],
+                ],
+                'startDate' => '2021-01-01T00:00:00+01:00',
+                'endDate' => '2021-01-02T00:00:00+01:00',
+            ],
+            $serializer->serialize()
+        );
+    }
+
+    /**
+     * @test
+     */
+    public function it_can_deserialize_a_calendar(): void
+    {
+        $data = [
+            'type' => 'multiple',
+            'status' => [
+                'type' => 'Available',
+            ],
+            'bookingAvailability' => [
+                'type' => 'Available',
+            ],
+            'timestamps' => [
+                0 => [
+                    'startDate' => '2021-01-01T00:00:00+01:00',
+                    'endDate' => '2021-01-02T00:00:00+01:00',
+                    'status' => [
+                        'type' => 'Available',
+                    ],
+                    'bookingAvailability' => [
+                        'type' => 'Available',
+                    ],
+                ],
+                1 => [
+                    'startDate' => '2021-01-04T00:00:00+01:00',
+                    'endDate' => '2021-01-05T00:00:00+01:00',
+                    'status' => [
+                        'type' => 'Available',
+                    ],
+                    'bookingAvailability' => [
+                        'type' => 'Available',
+                    ],
+                ],
+            ],
+            'startDate' => '2021-01-01T00:00:00+01:00',
+            'endDate' => '2021-01-05T00:00:00+01:00',
+        ];
+
+        $this->assertEquals(
+            new MultipleSubEventsCalendar(
+                new SubEvents(
+                    new SubEvent(
+                        new DateRange(
+                            new DateTimeImmutable('2021-01-01T00:00:00+01:00'),
+                            new DateTimeImmutable('2021-01-02T00:00:00+01:00')
+                        ),
+                        new Status(StatusType::Available()),
+                        BookingAvailability::Available()
+                    ),
+                    new SubEvent(
+                        new DateRange(
+                            new DateTimeImmutable('2021-01-04T00:00:00+01:00'),
+                            new DateTimeImmutable('2021-01-05T00:00:00+01:00')
+                        ),
+                        new Status(StatusType::Available()),
+                        BookingAvailability::Available()
+                    )
+                )
+            ),
+            CalendarSerializer::deserialize($data)
+        );
+    }
+
+    /**
+     * @test
+     */
+    public function it_falls_back_to_single_calendar_on_single_timestamp(): void
+    {
+        $data = [
+            'type' => 'multiple',
+            'status' => [
+                'type' => 'Available',
+            ],
+            'bookingAvailability' => [
+                'type' => 'Available',
+            ],
+            'timestamps' => [
+                0 => [
+                    'startDate' => '2021-01-01T00:00:00+01:00',
+                    'endDate' => '2021-01-02T00:00:00+01:00',
+                    'status' => [
+                        'type' => 'Available',
+                    ],
+                    'bookingAvailability' => [
+                        'type' => 'Available',
+                    ],
+                ],
+            ],
+            'startDate' => '2021-01-01T00:00:00+01:00',
+            'endDate' => '2021-01-02T00:00:00+01:00',
+        ];
+
+        $this->assertEquals(
+            new SingleSubEventCalendar(
+                new SubEvent(
+                    new DateRange(
+                        new DateTimeImmutable('2021-01-01T00:00:00+01:00'),
+                        new DateTimeImmutable('2021-01-02T00:00:00+01:00')
+                    ),
+                    new Status(StatusType::Available()),
+                    BookingAvailability::Available()
+                )
+            ),
+            CalendarSerializer::deserialize($data)
+        );
+    }
+
+    /**
+     * @test
+     */
+    public function it_upgrades_to_multiple_calendar_on_multiple_timestamp(): void
+    {
+        $data = [
+            'type' => 'single',
+            'status' => [
+                'type' => 'Available',
+            ],
+            'bookingAvailability' => [
+                'type' => 'Available',
+            ],
+            'timestamps' => [
+                0 => [
+                    'startDate' => '2021-01-01T00:00:00+01:00',
+                    'endDate' => '2021-01-02T00:00:00+01:00',
+                    'status' => [
+                        'type' => 'Available',
+                    ],
+                    'bookingAvailability' => [
+                        'type' => 'Available',
+                    ],
+                ],
+                1 => [
+                    'startDate' => '2021-01-04T00:00:00+01:00',
+                    'endDate' => '2021-01-05T00:00:00+01:00',
+                    'status' => [
+                        'type' => 'Available',
+                    ],
+                    'bookingAvailability' => [
+                        'type' => 'Available',
+                    ],
+                ],
+            ],
+            'startDate' => '2021-01-01T00:00:00+01:00',
+            'endDate' => '2021-01-05T00:00:00+01:00',
+        ];
+
+        $this->assertEquals(
+            new MultipleSubEventsCalendar(
+                new SubEvents(
+                    new SubEvent(
+                        new DateRange(
+                            new DateTimeImmutable('2021-01-01T00:00:00+01:00'),
+                            new DateTimeImmutable('2021-01-02T00:00:00+01:00')
+                        ),
+                        new Status(StatusType::Available()),
+                        BookingAvailability::Available()
+                    ),
+                    new SubEvent(
+                        new DateRange(
+                            new DateTimeImmutable('2021-01-04T00:00:00+01:00'),
+                            new DateTimeImmutable('2021-01-05T00:00:00+01:00')
+                        ),
+                        new Status(StatusType::Available()),
+                        BookingAvailability::Available()
+                    )
+                )
+            ),
+            CalendarSerializer::deserialize($data)
+        );
+    }
+}