diff --git a/src/NodaTimeSplitter.php b/src/NodaTimeSplitter.php
index 1432989..c3b1f98 100644
--- a/src/NodaTimeSplitter.php
+++ b/src/NodaTimeSplitter.php
@@ -470,8 +470,8 @@ final class NodaTimeSplitter {
         $datum = self::clean_input($datum);
 
         // 0000-0000
-        if (preg_match("/^[0-9][0-9][0-9][0-9](\-|\/)[0-9][0-9][0-9][0-9]$/", $datum)
-            || preg_match("/^[0-9][0-9][0-9][0-9](\-|\/)[0-9][0-9][0-9][0-9]\.$/", $datum)
+        if (preg_match("/^[0-9][0-9][0-9][0-9](\-|\/)[0-9][0-9][0-9][0-9]$/", $datum) !== false
+            || preg_match("/^[0-9][0-9][0-9][0-9](\-|\/)[0-9][0-9][0-9][0-9]\.$/", $datum) !== false
         ) {
             $start = substr($datum, 0, 4);
             $end = substr($datum, 5, 4);
@@ -667,7 +667,7 @@ final class NodaTimeSplitter {
      * @param string $start Begin time.
      * @param string $end   End time.
      *
-     * @return array<integer>
+     * @return array<string>
      */
     public static function negotiate_century_span_bce_ce(string $start, string $end):array {