diff --git a/lisp/progmodes/python.el b/lisp/progmodes/python.el
index eb17d075921..2e7410ac833 100644
--- a/lisp/progmodes/python.el
+++ b/lisp/progmodes/python.el
@@ -2268,7 +2268,7 @@ banner and the initial prompt are received separately."
       (while t
         (when (not (accept-process-output process timeout))
           (throw 'found nil))
-        (when (looking-back regexp)
+        (when (looking-back regexp (point-min))
           (throw 'found t))))))
 
 (defun python-shell-comint-end-of-output-p (output)