diff --git a/src/Dibi/HashMap.php b/src/Dibi/HashMap.php
index eef445f1..bdf1b693 100644
--- a/src/Dibi/HashMap.php
+++ b/src/Dibi/HashMap.php
@@ -58,7 +58,7 @@ final class HashMap extends HashMapBase
 	{
 		if ($nm == '') {
 			$nm = "\xFF";
-			return $this->$nm = $this->$nm ?? $this->getCallback()('');
+			return isset($this->$nm) ? $this->$nm : $this->$nm = $this->getCallback()('');
 		} else {
 			return $this->$nm = $this->getCallback()($nm);
 		}
diff --git a/tests/dibi/HashMap.phpt b/tests/dibi/HashMap.phpt
new file mode 100644
index 00000000..f14cfc1e
--- /dev/null
+++ b/tests/dibi/HashMap.phpt
@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+use Tester\Assert;
+
+require __DIR__ . '/bootstrap.php';
+
+$hash = new Dibi\HashMap(function ($v) {
+	return "b-$v-e";
+});
+
+Assert::same('b-X-e', $hash->{'X'});
+Assert::same('b--e', $hash->{''});