diff --git a/gallery_dl/extractor/pixiv.py b/gallery_dl/extractor/pixiv.py
index 1601031c..8aee0583 100644
--- a/gallery_dl/extractor/pixiv.py
+++ b/gallery_dl/extractor/pixiv.py
@@ -554,6 +554,7 @@ class PixivAppAPI():
         response = self.extractor.request(
             url, method="POST", headers=headers, data=data, fatal=False)
         if response.status_code >= 400:
+            self.log.debug(response.text)
             raise exception.AuthenticationError()
 
         data = response.json()["response"]