diff --git a/lib/Property/ICalendar/Recur.php b/lib/Property/ICalendar/Recur.php
index 9a1e9e643..10081673e 100644
--- a/lib/Property/ICalendar/Recur.php
+++ b/lib/Property/ICalendar/Recur.php
@@ -189,7 +189,14 @@ public static function stringToArray(string $value): array
             if (empty($part)) {
                 continue;
             }
-            list($partName, $partValue) = explode('=', $part);
+
+            $parts = explode('=', $part);
+
+            if (2 !== count($parts)) {
+                throw new InvalidDataException('The supplied iCalendar RRULE part is incorrect: '.$part);
+            }
+
+            list($partName, $partValue) = $parts;
 
             // The value itself had multiple values..
             if (false !== strpos($partValue, ',')) {
diff --git a/tests/VObject/Property/ICalendar/RecurTest.php b/tests/VObject/Property/ICalendar/RecurTest.php
index b2750f03b..29096e9de 100644
--- a/tests/VObject/Property/ICalendar/RecurTest.php
+++ b/tests/VObject/Property/ICalendar/RecurTest.php
@@ -4,6 +4,7 @@
 
 use PHPUnit\Framework\TestCase;
 use Sabre\VObject\Component\VCalendar;
+use Sabre\VObject\InvalidDataException;
 use Sabre\VObject\Node;
 use Sabre\VObject\Reader;
 
@@ -194,6 +195,15 @@ public function testValidateStripNoFreq(): void
         );
     }
 
+    public function testUnrepairableRRule(): void
+    {
+        $calendar = new VCalendar();
+
+        $this->expectException(InvalidDataException::class);
+
+        $property = $calendar->createProperty('RRULE', 'IAmNotARRule');
+    }
+
     public function testValidateInvalidByMonthRruleWithRepair(): void
     {
         $calendar = new VCalendar();