diff --git a/docs/configuration.rst b/docs/configuration.rst
index 1d8bd58e..00830db2 100644
--- a/docs/configuration.rst
+++ b/docs/configuration.rst
@@ -1107,6 +1107,16 @@ Description Certificate validation during file downloads.
 =========== =====
 
 
+downloader.http.adjust-extensions
+---------------------------------
+=========== =====
+Type        ``bool``
+Default     ``true``
+Description Check the file headers of ``jpg``, ``png``, and ``gif`` files
+            and adjust their filename extensions if they do not match.
+=========== =====
+
+
 downloader.ytdl.format
 ----------------------
 =========== =====
diff --git a/docs/gallery-dl.conf b/docs/gallery-dl.conf
index c75bfd27..2f7c58ea 100644
--- a/docs/gallery-dl.conf
+++ b/docs/gallery-dl.conf
@@ -155,6 +155,7 @@
 
         "http":
         {
+            "adjust-extensions": true,
             "mtime": true,
             "rate": null,
             "retries": 4,
diff --git a/gallery_dl/downloader/http.py b/gallery_dl/downloader/http.py
index 7a951916..bf8b3cbd 100644
--- a/gallery_dl/downloader/http.py
+++ b/gallery_dl/downloader/http.py
@@ -26,6 +26,7 @@ class HttpDownloader(DownloaderBase):
 
     def __init__(self, extractor, output):
         DownloaderBase.__init__(self, extractor, output)
+        self.adjust_extension = self.config("adjust-extensions", True)
         self.retries = self.config("retries", extractor._retries)
         self.timeout = self.config("timeout", extractor._timeout)
         self.verify = self.config("verify", extractor._verify)
@@ -59,7 +60,6 @@ class HttpDownloader(DownloaderBase):
 
     def _download_impl(self, url, pathfmt):
         response = None
-        adj_ext = None
         tries = 0
         msg = ""
 
@@ -152,13 +152,14 @@ class HttpDownloader(DownloaderBase):
                     continue
 
                 # check filename extension
-                adj_ext = self.check_extension(file, pathfmt)
+                if self.adjust_extension:
+                    adj_ext = self.check_extension(file, pathfmt)
+                    if adj_ext:
+                        pathfmt.set_extension(adj_ext)
 
             break
 
         self.downloading = False
-        if adj_ext:
-            pathfmt.set_extension(adj_ext)
         if self.mtime:
             pathfmt.keywords["_mtime"] = response.headers.get("Last-Modified")
         return True
diff --git a/test/test_results.py b/test/test_results.py
index dffc5e84..fe346c15 100644
--- a/test/test_results.py
+++ b/test/test_results.py
@@ -166,7 +166,6 @@ class ResultJob(job.DownloadJob):
 
         if content:
             self.fileobj = TestPathfmt(self.hash_content)
-            self.get_downloader("http").check_extension = lambda a, b: None
 
         self.format_directory = TestFormatter(
             "".join(self.extractor.directory_fmt))
@@ -278,6 +277,7 @@ def setup_test_config():
     config.clear()
     config.set(("cache", "file"), ":memory:")
     config.set(("downloader", "part"), False)
+    config.set(("downloader", "adjust-extensions"), False)
     config.set(("extractor", "timeout"), 60)
     config.set(("extractor", "username"), name)
     config.set(("extractor", "password"), name)