diff --git a/ext/pdo_firebird/tests/gh18276.phpt b/ext/pdo_firebird/tests/gh18276.phpt
new file mode 100644
index 0000000000000..b289f3b36470c
--- /dev/null
+++ b/ext/pdo_firebird/tests/gh18276.phpt
@@ -0,0 +1,41 @@
+--TEST--
+GH-18276 (persistent connection - setAttribute(Pdo\Firebird::ATTR_DATE_FORMAT, ..) results in "zend_mm_heap corrupted")
+--EXTENSIONS--
+pdo_firebird
+--SKIPIF--
+<?php require('skipif.inc'); ?>
+--XLEAK--
+A bug in firebird causes a memory leak when calling `isc_attach_database()`.
+See https://github.com/FirebirdSQL/firebird/issues/7849
+--FILE--
+<?php
+
+require("testdb.inc");
+unset($dbh);
+
+$dbh = new PDO(
+    PDO_FIREBIRD_TEST_DSN,
+    PDO_FIREBIRD_TEST_USER,
+    PDO_FIREBIRD_TEST_PASS,
+    [
+        PDO::ATTR_PERSISTENT => true,
+    ],
+);
+unset($dbh);
+
+$dbh = new PDO(
+    PDO_FIREBIRD_TEST_DSN,
+    PDO_FIREBIRD_TEST_USER,
+    PDO_FIREBIRD_TEST_PASS,
+    [
+        PDO::ATTR_PERSISTENT => true,
+    ],
+);
+$dbh->setAttribute(Pdo\firebird::ATTR_DATE_FORMAT, 'Y----m----d');
+$dbh->setAttribute(Pdo\firebird::ATTR_TIME_FORMAT, 'H::::i::::s');
+$dbh->setAttribute(Pdo\firebird::ATTR_TIMESTAMP_FORMAT, 'Y----m----d....H::::i::::s');
+
+echo 'done!';
+?>
+--EXPECT--
+done!