diff --git a/src/Factory/DbServiceFactory.php b/src/Factory/DbServiceFactory.php
index 94aec47d..b9888e21 100644
--- a/src/Factory/DbServiceFactory.php
+++ b/src/Factory/DbServiceFactory.php
@@ -201,7 +201,7 @@ private function getAdapterClass(string $phptype): string
      */
     private function buildConnectionConfig(array $sqlConfig): array
     {
-        return [
+        $config = [
             'username' => $sqlConfig['username'] ?? '',
             'password' => $sqlConfig['password'] ?? '',
             'database' => $sqlConfig['database'] ?? $sqlConfig['dbname'] ?? '',
@@ -209,5 +209,17 @@ private function buildConnectionConfig(array $sqlConfig): array
             'port' => $sqlConfig['port'] ?? 3306,
             'charset' => $sqlConfig['charset'] ?? 'UTF-8',
         ];
+
+        // Preserve Unix-socket connection settings when the config asks
+        // for them; without this the adapter falls back to the TCP
+        // host/port defaults above and breaks socket deployments.
+        if (isset($sqlConfig['protocol'])) {
+            $config['protocol'] = $sqlConfig['protocol'];
+        }
+        if (isset($sqlConfig['socket'])) {
+            $config['socket'] = $sqlConfig['socket'];
+        }
+
+        return $config;
     }
 }
diff --git a/test/Unit/Factory/DbServiceFactoryTest.php b/test/Unit/Factory/DbServiceFactoryTest.php
new file mode 100644
index 00000000..ead2ac7d
--- /dev/null
+++ b/test/Unit/Factory/DbServiceFactoryTest.php
@@ -0,0 +1,84 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * Copyright 2026 The Horde Project (http://www.horde.org/)
+ *
+ * See the enclosed file LICENSE for license information (LGPL). If you
+ * did not receive this file, see http://www.horde.org/licenses/lgpl21.
+ *
+ * @author Torben Dannhauer <torben@dannhauer.de>
+ * @category Horde
+ * @package  Core
+ * @license  http://www.horde.org/licenses/lgpl21 LGPL 2.1
+ */
+
+namespace Horde\Core\Test\Unit\Factory;
+
+use Horde\Core\Factory\DbServiceFactory;
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use ReflectionClass;
+
+#[CoversClass(DbServiceFactory::class)]
+final class DbServiceFactoryTest extends TestCase
+{
+    public function testBuildConnectionConfigPreservesUnixProtocol(): void
+    {
+        $config = $this->buildConnectionConfig([
+            'username' => 'horde',
+            'password' => 'secret',
+            'protocol' => 'unix',
+            'socket' => '/var/run/postgresql/.s.PGSQL.5432',
+            'database' => 'horde',
+            'phptype' => 'pgsql',
+        ]);
+
+        // The unix-socket keys reach the adapter untouched.
+        self::assertSame('unix', $config['protocol']);
+        self::assertSame('/var/run/postgresql/.s.PGSQL.5432', $config['socket']);
+        self::assertSame('horde', $config['database']);
+    }
+
+    public function testBuildConnectionConfigRenamesHostspecToHost(): void
+    {
+        $config = $this->buildConnectionConfig([
+            'username' => 'horde',
+            'password' => 'secret',
+            'hostspec' => 'db.example.test',
+            'port' => 5433,
+            'database' => 'horde',
+            'phptype' => 'pgsql',
+        ]);
+
+        self::assertSame('db.example.test', $config['host']);
+        self::assertArrayNotHasKey('hostspec', $config);
+        self::assertSame(5433, $config['port']);
+    }
+
+    public function testBuildConnectionConfigDefaultsCharset(): void
+    {
+        $config = $this->buildConnectionConfig([
+            'username' => 'horde',
+            'password' => 'secret',
+            'database' => 'horde',
+            'phptype' => 'mysqli',
+        ]);
+
+        self::assertSame('UTF-8', $config['charset']);
+    }
+
+    /**
+     * @param array<string, mixed> $sqlConfig
+     * @return array<string, mixed>
+     */
+    private function buildConnectionConfig(array $sqlConfig): array
+    {
+        $factory = new DbServiceFactory();
+        $method = (new ReflectionClass($factory))->getMethod('buildConnectionConfig');
+        $method->setAccessible(true);
+
+        return $method->invoke($factory, $sqlConfig);
+    }
+}