diff --git a/src/NodaTimeSplitter.php b/src/NodaTimeSplitter.php
index c3b1f98..8eb0d22 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]$/", $datum) !== false
-            || preg_match("/^[0-9][0-9][0-9][0-9](\-|\/)[0-9][0-9][0-9][0-9]\.$/", $datum) !== false
+        if (!empty(preg_match("/^[0-9][0-9][0-9][0-9](\-|\/)[0-9][0-9][0-9][0-9]$/", $datum))
+            || !empty(preg_match("/^[0-9][0-9][0-9][0-9](\-|\/)[0-9][0-9][0-9][0-9]\.$/", $datum))
         ) {
             $start = substr($datum, 0, 4);
             $end = substr($datum, 5, 4);