diff --git a/src/UriTemplate.php b/src/UriTemplate.php
index 659168fe..248d2272 100644
--- a/src/UriTemplate.php
+++ b/src/UriTemplate.php
@@ -402,7 +402,9 @@ private function expandExpression(array $foundExpression): string
         $parts = [];
         /** @var array{name:string, modifier:string, position:string} $variable */
         foreach ($expression['variables'] as $variable) {
-            $parts[] = $this->expandVariable($variable, $expression['operator'], $joiner, $useQuery);
+            if (isset($this->variables[$variable['name']])) {
+                $parts[] = $this->expandVariable($variable, $expression['operator'], $joiner, $useQuery);
+            }
         }
 
         $nullFilter = static function ($value): bool {
diff --git a/tests/UriTemplateTest.php b/tests/UriTemplateTest.php
index 7b9c3607..45140f62 100644
--- a/tests/UriTemplateTest.php
+++ b/tests/UriTemplateTest.php
@@ -224,6 +224,7 @@ public function templateExpansionProvider(): iterable
                 ['{;x,y,empty}',        ';x=1024;y=768;empty'],
                 ['{?x,y}',              '?x=1024&y=768'],
                 ['{?x,y,empty}',        '?x=1024&y=768&empty='],
+                ['{?x,y,undef}',        '?x=1024&y=768'],
                 ['?fixed=yes{&x}',      '?fixed=yes&x=1024'],
                 ['{&x,y,empty}',        '&x=1024&y=768&empty='],
             ],