diff --git a/src/execo/process.py b/src/execo/process.py
index fcd19aaee0bd74ab37bc6fe1b14169a89ca0ebac..6eff553e779b3fb14b097e10694d3ec351444792 100644
--- a/src/execo/process.py
+++ b/src/execo/process.py
@@ -319,6 +319,7 @@ class ExpectOutputHandler(ProcessOutputHandler):
                     self.callback(process, stream, re_index, mo)
 
     def read(self, process, stream, string, eof, error):
+        logger.debug("ExpectOuputHandler: stream %s of process %s: read %r" % (stream, process, string))
         self._scan(process, stream, string, eof, error)
 
 class ProcessBase(object):