diff --git a/lib/DateTimeParser.php b/lib/DateTimeParser.php
index 4a71931a..5ce9f207 100644
--- a/lib/DateTimeParser.php
+++ b/lib/DateTimeParser.php
@@ -93,7 +93,7 @@ public static function parseDuration(string $duration): \DateInterval
 
         $invert = false;
 
-        if ('-' === $matches['plusminus']) {
+        if (isset($matches['plusminus']) && '-' === $matches['plusminus']) {
             $invert = true;
         }
 
diff --git a/tests/VObject/DateTimeParserTest.php b/tests/VObject/DateTimeParserTest.php
index b1e7f7cd..cdf0fe99 100644
--- a/tests/VObject/DateTimeParserTest.php
+++ b/tests/VObject/DateTimeParserTest.php
@@ -34,6 +34,12 @@ public function testParseICalendarDurationDateInterval(): void
         self::assertEquals($expected, DateTimeParser::parseDuration('-PT3M'));
     }
 
+    public function testParseDurationZero(): void
+    {
+        $expected = new \DateInterval('PT0S');
+        self::assertEquals($expected, DateTimeParser::parseDuration('P'));
+    }
+
     public function testParseICalendarDurationFail(): void
     {
         $this->expectException(InvalidDataException::class);