diff --git a/src/tracelog.rs b/src/tracelog.rs
index 799f205..c4915ff 100644
--- a/src/tracelog.rs
+++ b/src/tracelog.rs
@@ -15,8 +15,11 @@ impl Logger {
         Logger(None)
     }
 
+    /// Truncates any existing file at `path` -- each run starts a fresh
+    /// log, so a re-run never leaves stale lines from a previous attempt
+    /// mixed in with (or mistaken for) the current one.
     pub fn open(path: &Path) -> std::io::Result<Logger> {
-        let f = OpenOptions::new().create(true).append(true).open(path)?;
+        let f = OpenOptions::new().create(true).write(true).truncate(true).open(path)?;
         Ok(Logger(Some(Mutex::new(f))))
     }