diff --git a/ext/pdo_firebird/firebird_driver.c b/ext/pdo_firebird/firebird_driver.c
index 5db0c7f75aa1..2dc0755a6146 100644
--- a/ext/pdo_firebird/firebird_driver.c
+++ b/ext/pdo_firebird/firebird_driver.c
@@ -681,6 +681,14 @@ static bool firebird_handle_preparer(pdo_dbh_t *dbh, zend_string *sql, /* {{{ */
 			if (isc_dsql_describe_bind(H->isc_status, &s, PDO_FB_SQLDA_VERSION, S->in_sqlda)) {
 				break;
 			}
+
+			/* make all parameters nullable */
+			unsigned int i;
+			XSQLVAR* var;			
+			for (i = 0, var = S->in_sqlda->sqlvar; i < S->in_sqlda->sqld; i++, var++) {
+				/* The low bit of sqltype indicates that the parameter can take a NULL value */
+				var->sqltype |= 1;
+			}
 		}
 
 		stmt->driver_data = S;
diff --git a/ext/pdo_firebird/tests/bug_15604.phpt b/ext/pdo_firebird/tests/bug_15604.phpt
new file mode 100644
index 000000000000..52ab04d18af6
--- /dev/null
+++ b/ext/pdo_firebird/tests/bug_15604.phpt
@@ -0,0 +1,78 @@
+--TEST--
+Bug #15604 It is not possible to pass a NULL value as an input parameter if the field is marked as NOT NULL.
+--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_once 'testdb.inc';
+
+$dbh = getDbConnection();
+
+$dbh->exec('
+recreate table t_bug_15604 (
+  id bigint not null,
+  a int not null,
+  b int,
+  constraint pk_bug_15604 primary key(id)
+)
+');
+
+$dbh->exec('recreate sequence g_bug_15604');
+
+$dbh->exec(<<<'SQL'
+create or alter trigger t_bug_15604_bi0 for t_bug_15604
+active before insert position 0
+as
+begin
+  if (new.id is null) then
+    new.id = next value for g_bug_15604;
+end
+SQL
+);
+
+$stmt = $dbh->prepare('insert into t_bug_15604(id, a, b) values(?, ?, ?)');
+$stmt->execute([null, 1, 2]);
+$stmt->execute([2, 2, null]);
+unset($stmt);
+
+$stmt2 = $dbh->prepare('SELECT id, a, b FROM t_bug_15604 WHERE id = ?');
+
+$stmt2->execute([null]); 
+$data = $stmt2->fetch(\PDO::FETCH_ASSOC);
+$stmt2->closeCursor();
+var_dump($data);
+
+$stmt2->execute([2]); 
+$data = $stmt2->fetch(\PDO::FETCH_ASSOC);
+$stmt2->closeCursor();
+var_dump($data);
+
+unset($stmt2);
+
+echo "\nOK\n";
+?>
+--CLEAN--
+<?php
+require_once 'testdb.inc';
+$dbh = getDbConnection();
+@$dbh->exec('drop table t_bug_15604');
+@$dbh->exec('drop sequence g_bug_15604');
+unset($dbh);
+?>
+--EXPECT--
+bool(false)
+array(3) {
+  ["ID"]=>
+  int(2)
+  ["A"]=>
+  int(2)
+  ["B"]=>
+  NULL
+}
+
+OK