diff --git a/src/book.cpp b/src/book.cpp
index d5bab90b..1dd5aa6d 100644
--- a/src/book.cpp
+++ b/src/book.cpp
@@ -383,7 +383,7 @@ bool Book::open(const char* fName) {
       return false; // Silently fail if the file is not found
 
   // Get the book size in number of entries, we are already at the end of file
-  size = tellg() / sizeof(BookEntry);
+  size = (size_t)tellg() / sizeof(BookEntry);
 
   if (!good())
   {