diff --git a/src/book.cpp b/src/book.cpp
index 0fff6827..fbb1984c 100644
--- a/src/book.cpp
+++ b/src/book.cpp
@@ -420,7 +420,7 @@ Move Book::probe(const Position& pos, const string& fName, bool pickBest) {
       // Choose book move according to its score. If a move has a very
       // high score it has higher probability to be choosen than a move
       // with lower score. Note that first entry is always chosen.
-      if (   (RKiss.rand<unsigned>() % sum < e.count)
+      if (   (sum && RKiss.rand<unsigned>() % sum < e.count)
           || (pickBest && e.count == best))
           move = Move(e.move);
   }