diff --git a/include/manager.h b/include/manager.h
index d6e0144d..6fb74d22 100644
--- a/include/manager.h
+++ b/include/manager.h
@@ -129,7 +129,7 @@ class Manager
    *
    * @return The id of the current book (or empty string if no current book).
    */
-  string getCurrentBookId();
+  string getCurrentBookId() const;
 
   /**
    * Set the path of the external fulltext index associated to a book.
diff --git a/src/manager.cpp b/src/manager.cpp
index 72b0f8ea..b0e307c5 100644
--- a/src/manager.cpp
+++ b/src/manager.cpp
@@ -243,7 +243,7 @@ bool Manager::setCurrentBookId(const string id)
   return true;
 }
 
-string Manager::getCurrentBookId()
+string Manager::getCurrentBookId() const
 {
   return library.current.empty() ? "" : library.current.top();
 }