diff --git a/src/book.hpp b/src/book.hpp
index 4404299..cfc6125 100644
--- a/src/book.hpp
+++ b/src/book.hpp
@@ -57,10 +57,10 @@ struct book
 [[nodiscard]] document process_page(std::string_view text);
 
 //! Return last headline if possible.
-[[nodiscard]] std::string headline(const document &doc, size_t pos);
+[[nodiscard]] string headline(const document &doc, size_t pos);
 
 //! Return current page if possible.
-[[nodiscard]] std::string page(const document &doc, size_t pos);
+[[nodiscard]] string page(const document &doc, size_t pos);
 
 //! Returns the file path of the OPF file in the EPUB.
 [[nodiscard]] fs::path get_opf_file_path(const fs::path &zipfile);