diff --git a/core/fpdfapi/parser/cpdf_linearized_header.cpp b/core/fpdfapi/parser/cpdf_linearized_header.cpp
index 994d69f..5032bc3 100644
--- a/core/fpdfapi/parser/cpdf_linearized_header.cpp
+++ b/core/fpdfapi/parser/cpdf_linearized_header.cpp
@@ -43,6 +43,7 @@
   return header->GetFileSize() == file_size &&
          static_cast<int>(header->GetFirstPageNo()) >= 0 &&
          header->GetFirstPageNo() < kMaxInt &&
+         header->GetFirstPageNo() < header->GetPageCount() &&
          header->GetMainXRefTableFirstEntryOffset() < file_size &&
          header->GetPageCount() > 0 &&
          header->GetFirstPageEndOffset() < file_size &&