diff --git a/src/calibre/gui2/tts/piper.py b/src/calibre/gui2/tts/piper.py
index 1de1a53625..1f44c04da1 100644
--- a/src/calibre/gui2/tts/piper.py
+++ b/src/calibre/gui2/tts/piper.py
@@ -31,6 +31,7 @@ def debug(*a, **kw):
         if not hasattr(debug, 'first'):
             debug.first = monotonic()
         kw['end'] = kw.get('end', '\r\n')
+        kw['flush'] = True
         print(f'[{monotonic() - debug.first:.2f}]', *a, **kw)