1 files changed, 5 insertions, 1 deletions
diff --git a/src/times.h b/src/times.h
index cc980858..421d1462 100644
--- a/src/times.h
+++ b/src/times.h
@@ -500,7 +500,11 @@ public:
   void   stabilize(const optional<date_t>& date = none);
 
   bool   is_valid() const {
-    return start != boost::none;
+#if BOOST_VERSION >= 105600
+    return start != NULL;
+#else
+    return start;
+#endif
   }
 
   /** Find the current or next period containing date.  Returns false if