diff --git a/playa/worker.py b/playa/worker.py
index c39095d..a645c0d 100644
--- a/playa/worker.py
+++ b/playa/worker.py
@@ -81,7 +81,7 @@ def _deref_document(ref: DocumentRef) -> "Document":
 
 
 def _ref_page(page: "Page") -> PageRef:
-    return page.doc, page.page_idx
+    return _ref_document(page.doc), page.page_idx
 
 
 def _deref_page(ref: PageRef) -> "Page":
diff --git a/tests/test_parallel.py b/tests/test_parallel.py
index 7f2c7e2..42147ad 100644
--- a/tests/test_parallel.py
+++ b/tests/test_parallel.py
@@ -1,10 +1,13 @@
 """Test parallel analysis."""
 
+import operator
+from typing import List
+
 import pytest
 
 import playa
 import playa.document
-from playa.page import Page
+from playa.page import Page, XObjectObject
 from playa.worker import in_worker, _get_document
 from tests.data import TESTDIR, CONTRIB
 
@@ -30,22 +33,33 @@ def test_open_parallel():
         assert future.result() == 1
 
 
-def get_resources(page: Page) -> dict:
-    assert in_worker()
-    return page.resources
-
-
 def test_parallel_references():
     with playa.open(
         TESTDIR / "pdf_structure.pdf", space="default", max_workers=2
     ) as pdf:
-        (resources,) = list(pdf.pages.map(get_resources))
+        (resources,) = pdf.pages.map(operator.attrgetter("resources"))
         desc = resources["Font"].resolve()  # should succeed!
         assert "F1" in desc  # should exist!
         assert "F2" in desc
         assert desc["F1"].resolve()["LastChar"] == 17
 
 
+def get_xobjs(page: Page) -> List[XObjectObject]:
+    return list(page.xobjects)
+
+
+@pytest.mark.skipif(not CONTRIB.exists(), reason="contrib samples not present")
+def test_parallel_xobjects():
+    # Verify that page references (used in XObjects) also work
+    with playa.open(CONTRIB / "basicapi.pdf", space="default", max_workers=2) as pdf:
+        for page in pdf.pages:
+            for xobj in page.xobjects:
+                assert xobj.page.page_idx == page.page_idx
+        for idx, xobjs in enumerate(pdf.pages.map(get_xobjs)):
+            for xobj in xobjs:
+                assert xobj.page.page_idx == idx
+
+
 def get_text(page: Page) -> str:
     return " ".join(x.chars for x in page.texts)
 
@@ -60,4 +74,4 @@ def test_map_parallel():
 
 
 if __name__ == "__main__":
-    test_parallel_references()
+    test_parallel_xobjects()