diff --git a/copyparty/httpcli.py b/copyparty/httpcli.py
index 93e52b13..536d4a40 100644
--- a/copyparty/httpcli.py
+++ b/copyparty/httpcli.py
@@ -298,7 +298,7 @@ class HttpCli(object):
 
         # default to utf8 html if no content-type is set
         if not mime:
-            mime = self.out_headers.get("Content-Type", "text/html; charset=UTF-8")
+            mime = self.out_headers.get("Content-Type", "text/html; charset=utf-8")
 
         self.out_headers["Content-Type"] = mime
 
@@ -1462,7 +1462,7 @@ class HttpCli(object):
             self.permit_caching()
 
         if "txt" in self.uparam:
-            mime = "text/plain; charset={}".format(self.uparam["txt"] or "UTF-8")
+            mime = "text/plain; charset={}".format(self.uparam["txt"] or "utf-8")
         else:
             mime = guess_mime(req_path)
 
@@ -1905,7 +1905,7 @@ class HttpCli(object):
                 for x in y
             ]
             ret = "\n".join(ret)
-            mime = "text/plain; charset=UTF-8"
+            mime = "text/plain; charset=utf-8"
         else:
             [x.pop(k) for k in ["name", "dt"] for y in [dirs, files] for x in y]
 
diff --git a/copyparty/util.py b/copyparty/util.py
index 130c7518..19d96bf6 100644
--- a/copyparty/util.py
+++ b/copyparty/util.py
@@ -100,7 +100,7 @@ IMPLICATIONS = [
 
 
 MIMES = {
-    "md": "text/plain; charset=UTF-8",
+    "md": "text/plain; charset=utf-8",
     "opus": "audio/ogg; codecs=opus",
     "webp": "image/webp",
 }
@@ -1284,7 +1284,7 @@ def guess_mime(url, fallback="application/octet-stream"):
 
     if ";" not in ret:
         if ret.startswith("text/") or ret.endswith("/javascript"):
-            ret += "; charset=UTF-8"
+            ret += "; charset=utf-8"
 
     return ret