diff --git a/scrapy/http/response/text.py b/scrapy/http/response/text.py
index 73bb811de..d580a7876 100644
--- a/scrapy/http/response/text.py
+++ b/scrapy/http/response/text.py
@@ -100,11 +100,13 @@ class TextResponse(Response):
     @memoizemethod_noargs
     def _headers_encoding(self):
         content_type = self.headers.get(b"Content-Type", b"")
-        return http_content_type_encoding(to_unicode(content_type))
+        return http_content_type_encoding(to_unicode(content_type, encoding="latin-1"))
 
     def _body_inferred_encoding(self):
         if self._cached_benc is None:
-            content_type = to_unicode(self.headers.get(b"Content-Type", b""))
+            content_type = to_unicode(
+                self.headers.get(b"Content-Type", b""), encoding="latin-1"
+            )
             benc, ubody = html_to_unicode(
                 content_type,
                 self.body,
diff --git a/scrapy/responsetypes.py b/scrapy/responsetypes.py
index f01e9096c..58884f21a 100644
--- a/scrapy/responsetypes.py
+++ b/scrapy/responsetypes.py
@@ -51,7 +51,9 @@ class ResponseTypes:
         header"""
         if content_encoding:
             return Response
-        mimetype = to_unicode(content_type).split(";")[0].strip().lower()
+        mimetype = (
+            to_unicode(content_type, encoding="latin-1").split(";")[0].strip().lower()
+        )
         return self.from_mimetype(mimetype)
 
     def from_content_disposition(self, content_disposition):