1 files changed, 1 insertions, 1 deletions
diff --git a/src/times.h b/src/times.h
index 2a5b9277..d2f7bb19 100644
--- a/src/times.h
+++ b/src/times.h
@@ -568,7 +568,7 @@ public:
   void   stabilize(const optional<date_t>& date = none);
 
   bool   is_valid() const {
-    return start;
+    return start != NULL;
   }
 
   /** Find the current or next period containing date.  Returns false if