diff --git a/z/entry.go b/z/entry.go
index d02660e..0af8945 100644
--- a/z/entry.go
+++ b/z/entry.go
@@ -41,6 +41,10 @@ func NewEntry(
     }
   }
 
+  if finishTime.Before(beginTime) && finishTime.IsZero() == false {
+    return Entry{}, errors.New("Beginning time of tracking cannot be after the finish time!")
+  }
+
   return Entry{
     id,
     beginTime,