diff --git a/core/fpdfapi/page/cpdf_image.h b/core/fpdfapi/page/cpdf_image.h
index 04355a9..ebda040 100644
--- a/core/fpdfapi/page/cpdf_image.h
+++ b/core/fpdfapi/page/cpdf_image.h
@@ -36,6 +36,8 @@
   RetainPtr<const CPDF_Dictionary> GetDict() const;
   RetainPtr<const CPDF_Stream> GetStream() const;
   RetainPtr<const CPDF_Dictionary> GetOC() const;
+
+  // Never returns nullptr.
   CPDF_Document* GetDocument() const { return m_pDocument; }
 
   int32_t GetPixelHeight() const { return m_Height; }
diff --git a/core/fpdfapi/page/cpdf_imageobject.cpp b/core/fpdfapi/page/cpdf_imageobject.cpp
index c031502..0511a02 100644
--- a/core/fpdfapi/page/cpdf_imageobject.cpp
+++ b/core/fpdfapi/page/cpdf_imageobject.cpp
@@ -82,10 +82,6 @@
   if (!m_pImage)
     return;
 
-  auto* pDoc = m_pImage->GetDocument();
-  if (!pDoc)
-    return;
-
   RetainPtr<const CPDF_Stream> pStream = m_pImage->GetStream();
   if (!pStream)
     return;
@@ -94,6 +90,9 @@
   if (!objnum)
     return;
 
+  auto* pDoc = m_pImage->GetDocument();
+  CHECK(pDoc);
+
   m_pImage.Reset();  // Clear my reference before asking the cache.
   pDoc->MaybePurgeImage(objnum);
 }