diff --git a/devlib/collector/serial_trace.py b/devlib/collector/serial_trace.py
index 4abceb9..5b538e7 100644
--- a/devlib/collector/serial_trace.py
+++ b/devlib/collector/serial_trace.py
@@ -54,7 +54,7 @@ class SerialTraceCollector(CollectorBase):
         if self.output_path is None:
             raise RuntimeError("Output path was not set.")
 
-        self._outfile_fh = open(self.output_path, 'w')
+        self._outfile_fh = open(self.output_path, 'wb')
         start_marker = "-------- Starting serial logging --------\n"
         self._outfile_fh.write(start_marker.encode('utf-8'))