diff --git a/gallery_dl/extractor/mangadex.py b/gallery_dl/extractor/mangadex.py
index e205379b4bd..e668ed26059 100644
--- a/gallery_dl/extractor/mangadex.py
+++ b/gallery_dl/extractor/mangadex.py
@@ -34,11 +34,6 @@ class MangadexChapterExtractor(MangadexExtractor, ChapterExtractor):
             "count": 64,
             "keyword": "1f6fb237a96cdf05b436ae2a37a4436e717bbb30",
         }),
-        # abnormal chapter string ("Vol. 1 Ch. 6 \ 5.1")
-        ("https://mangadex.org/chapter/255540", {
-            "count": 27,
-            "keyword": "fe5e3ece1bc6463350fde36f7e47e29d093fed84",
-        }),
         # NotFoundError
         ("https://mangadex.org/chapter/1", {
             "exception": exception.NotFoundError,
diff --git a/gallery_dl/extractor/simplyhentai.py b/gallery_dl/extractor/simplyhentai.py
index 326150bb4a9..2e1d8cb4be8 100644
--- a/gallery_dl/extractor/simplyhentai.py
+++ b/gallery_dl/extractor/simplyhentai.py
@@ -69,7 +69,8 @@ def get_metadata(self, page):
         }
 
     def get_images(self, _):
-        images = self.request(self.url + "/all-pages.json").json()
+        headers = {"Accept": "application/json"}
+        images = self.request(self.url + "/all-pages", headers=headers).json()
         return [
             (urls["full"], {"image_id": text.parse_int(image_id)})
             for image_id, urls in sorted(images.items())
diff --git a/test/test_results.py b/test/test_results.py
index 0a604f0805b..29754b48d04 100644
--- a/test/test_results.py
+++ b/test/test_results.py
@@ -22,6 +22,7 @@
 
 # temporary issues, etc.
 BROKEN = {
+    "dokireader",  # server down
 }