diff --git a/src/Psalm/Config/FileFilter.php b/src/Psalm/Config/FileFilter.php
index 8ca44094724..4ef5f993c4c 100644
--- a/src/Psalm/Config/FileFilter.php
+++ b/src/Psalm/Config/FileFilter.php
@@ -336,7 +336,7 @@ public static function loadFromArray(
             foreach ($config['referencedFunction'] as $referenced_function) {
                 $function_id = $referenced_function['name'] ?? '';
                 if (!is_string($function_id)
-                    || (!preg_match('/^[a-zA-Z_\x80-\xff][a-zA-Z0-9_\x80-\xff]*$/', $function_id)
+                    || (!preg_match('/^[a-zA-Z_\x80-\xff](?:[\\\\]?[a-zA-Z0-9_\x80-\xff]+)*$/', $function_id)
                         && !preg_match('/^[^:]+::[^:]+$/', $function_id) // methods are also allowed
                         && !static::isRegularExpression($function_id))) {
                     throw new ConfigException(
diff --git a/tests/Config/ConfigTest.php b/tests/Config/ConfigTest.php
index da14fa40fcf..c4b682967b3 100644
--- a/tests/Config/ConfigTest.php
+++ b/tests/Config/ConfigTest.php
@@ -18,6 +18,7 @@
 use Psalm\Internal\RuntimeCaches;
 use Psalm\Internal\Scanner\FileScanner;
 use Psalm\Issue\TooManyArguments;
+use Psalm\Issue\UndefinedFunction;
 use Psalm\Tests\Config\Plugin\FileTypeSelfRegisteringPlugin;
 use Psalm\Tests\Internal\Provider\FakeParserCacheProvider;
 use Psalm\Tests\TestCase;
@@ -1856,4 +1857,34 @@ public function testReferencedFunctionAllowsMethods(): void
             ),
         );
     }
+
+    public function testReferencedFunctionAllowsNamespacedFunctions(): void
+    {
+        $config_xml = Config::loadFromXML(
+            (string) getcwd(),
+            <<<XML
+            <?xml version="1.0"?>
+            <psalm>
+                <issueHandlers>
+                    <UndefinedFunction>
+                        <errorLevel type="suppress">
+                            <referencedFunction name="Foo\Bar\baz" />
+                        </errorLevel>
+                    </UndefinedFunction>
+                </issueHandlers>
+            </psalm>
+            XML,
+        );
+
+        $this->assertSame(
+            Config::REPORT_SUPPRESS,
+            $config_xml->getReportingLevelForIssue(
+                new UndefinedFunction(
+                    'Function Foo\Bar\baz does not exist',
+                    new Raw('aaa', 'aaa.php', 'aaa.php', 1, 2),
+                    'foo\bar\baz',
+                ),
+            ),
+        );
+    }
 }