diff --git a/include/library.h b/include/library.h
index 7211a843f..046329742 100644
--- a/include/library.h
+++ b/include/library.h
@@ -24,6 +24,7 @@
 #include <vector>
 #include <map>
 #include <memory>
+#include <mutex>
 #include <zim/archive.h>
 
 #include "book.h"
@@ -139,12 +140,14 @@ private: // functions
     bool accept(const Book& book) const;
 };
 
-
 /**
- * A Library store several books.
+ * This class is not part of the libkiwix API. Its only purpose is
+ * to simplify the implementation of the Library's move operations
+ * and avoid bugs should new data members be added to Library.
  */
-class Library
+class LibraryBase
 {
+protected: // data
   std::map<std::string, kiwix::Book> m_books;
   std::map<std::string, std::shared_ptr<Reader>> m_readers;
   std::map<std::string, std::shared_ptr<zim::Archive>> m_archives;
@@ -152,6 +155,22 @@ class Library
   class BookDB;
   std::unique_ptr<BookDB> m_bookDB;
 
+protected: // functions
+  LibraryBase();
+  ~LibraryBase();
+
+  LibraryBase(LibraryBase&& );
+  LibraryBase& operator=(LibraryBase&& );
+};
+
+/**
+ * A Library store several books.
+ */
+class Library : private LibraryBase
+{
+  // all data fields must be added in LibraryBase
+  mutable std::mutex m_mutex;
+
  public:
   typedef std::vector<std::string> BookIdCollection;
   typedef std::map<std::string, int> AttributeCounts;
diff --git a/src/library.cpp b/src/library.cpp
index e7afad696..616e004b1 100644
--- a/src/library.cpp
+++ b/src/library.cpp
@@ -58,21 +58,39 @@ bool booksReferToTheSameArchive(const Book& book1, const Book& book2)
 
 } // unnamed namespace
 
-class Library::BookDB : public Xapian::WritableDatabase
+class LibraryBase::BookDB : public Xapian::WritableDatabase
 {
 public:
   BookDB() : Xapian::WritableDatabase("", Xapian::DB_BACKEND_INMEMORY) {}
 };
 
-/* Constructor */
-Library::Library()
+LibraryBase::LibraryBase()
   : m_bookDB(new BookDB)
 {
 }
 
-Library::Library(Library&& ) = default;
+LibraryBase::~LibraryBase()
+{
+}
 
-Library& Library::operator=(Library&& ) = default;
+LibraryBase::LibraryBase(LibraryBase&& ) = default;
+LibraryBase& LibraryBase::operator=(LibraryBase&& ) = default;
+
+/* Constructor */
+Library::Library()
+{
+}
+
+Library::Library(Library&& other)
+  : LibraryBase(std::move(other))
+{
+}
+
+Library& Library::operator=(Library&& other)
+{
+  LibraryBase::operator=(std::move(other));
+  return *this;
+}
 
 /* Destructor */
 Library::~Library()