diff --git a/constants/annotation_common.h b/constants/annotation_common.h
index 8973360..471d244 100644
--- a/constants/annotation_common.h
+++ b/constants/annotation_common.h
@@ -23,6 +23,8 @@
 constexpr char kAS[] = "AS";
 constexpr char kBorder[] = "Border";
 constexpr char kC[] = "C";
+constexpr char kStructParent[] = "StructParent";
+constexpr char kOC[] = "OC";
 
 }  // namespace annotation
 }  // namespace pdfium
diff --git a/core/fpdfdoc/cpdf_annotlist.cpp b/core/fpdfdoc/cpdf_annotlist.cpp
index 748e1ee..c37c9ef 100644
--- a/core/fpdfdoc/cpdf_annotlist.cpp
+++ b/core/fpdfdoc/cpdf_annotlist.cpp
@@ -234,7 +234,8 @@
       const CPDF_Dictionary* pAnnotDict = pAnnot->GetAnnotDict();
       const CPDF_OCContext* pOCContext = pOptions->GetOCContext();
       if (pAnnotDict && pOCContext &&
-          !pOCContext->CheckOCGVisible(pAnnotDict->GetDictFor("OC"))) {
+          !pOCContext->CheckOCGVisible(
+              pAnnotDict->GetDictFor(pdfium::annotation::kOC))) {
         continue;
       }
     }