diff --git a/content-dpr/resources/dpr.py b/content-dpr/resources/dpr.py
index 14d7d550fe28d4..969ac2458d8b5a 100644
--- a/content-dpr/resources/dpr.py
+++ b/content-dpr/resources/dpr.py
@@ -1,24 +1,26 @@
+from wptserve.utils import isomorphic_decode
+
 def main(request, response):
     """
     Simple handler that sets a response header based on which client hint
     request headers were received.
     """
 
-    response.headers.append("Access-Control-Allow-Origin", "*")
+    response.headers.append(b"Access-Control-Allow-Origin", b"*")
     values = request.GET
-    name = values.first('name')
-    type = values.first('mimeType')
-    dpr = values.first('dpr')
+    name = values.first(b'name')
+    type = values.first(b'mimeType')
+    dpr = values.first(b'dpr')
     double = None
-    if 'double' in values:
-        double = values.first('double')
-    image_path = request.doc_root + "/".join(request.url_parts[2].split("/")[:-1]) + "/" + name
+    if b'double' in values:
+        double = values.first(b'double')
+    image_path = request.doc_root + u"/".join(request.url_parts[2].split(u"/")[:-1]) + u"/" + isomorphic_decode(name)
     f = open(image_path, "rb")
     buff = f.read()
     f.close()
-    response.headers.set("Content-Type", type)
-    response.headers.set("Content-DPR", dpr)
+    response.headers.set(b"Content-Type", type)
+    response.headers.set(b"Content-DPR", dpr)
     if double:
-        response.headers.append("Content-DPR", double)
-    response.headers.set("Content-Length", len(buff))
+        response.headers.append(b"Content-DPR", double)
+    response.headers.set(b"Content-Length", len(buff))
     response.content = buff
diff --git a/mimesniff/mime-types/resources/mime-charset.py b/mimesniff/mime-types/resources/mime-charset.py
index a4f90f52c323fc..46d8252e0c90a7 100644
--- a/mimesniff/mime-types/resources/mime-charset.py
+++ b/mimesniff/mime-types/resources/mime-charset.py
@@ -1,5 +1,7 @@
+from wptserve.utils import isomorphic_encode
+
 def main(request, response):
-    content = "<meta charset=utf-8>\n<script>document.write(document.characterSet)</script>"
+    content = b"<meta charset=utf-8>\n<script>document.write(document.characterSet)</script>"
 
     # This uses the following rather than
     #   response.headers.set("Content-Type", request.GET.first("type"));
@@ -7,10 +9,10 @@ def main(request, response):
     # to work around https://github.com/web-platform-tests/wpt/issues/8372.
 
     response.add_required_headers = False
-    output =  "HTTP/1.1 200 OK\r\n"
-    output += "Content-Length: " + str(len(content)) + "\r\n"
-    output += "Content-Type: " + request.GET.first("type") + "\r\n"
-    output += "\r\n"
+    output = b"HTTP/1.1 200 OK\r\n"
+    output += b"Content-Length: " + isomorphic_encode(str(len(content))) + b"\r\n"
+    output += b"Content-Type: " + request.GET.first(b"type") + b"\r\n"
+    output += b"\r\n"
     output += content
     response.writer.write(output)
     response.close_connection = True