diff --git a/swh/web/browse/utils.py b/swh/web/browse/utils.py
--- a/swh/web/browse/utils.py
+++ b/swh/web/browse/utils.py
@@ -1,4 +1,4 @@
-# Copyright (C) 2017-2019  The Software Heritage developers
+# Copyright (C) 2017-2020  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU Affero General Public License version 3, or any later version
 # See top-level LICENSE file for more information
@@ -280,14 +280,16 @@
 
     if mime_type.startswith('image/'):
         if mime_type in _browsers_supported_image_mimes:
-            content_data = base64.b64encode(content_data)
-            content_data = content_data.decode('utf-8')
+            content_data = base64.b64encode(content_data).decode('ascii')
         else:
             content_data = None
 
     if mime_type.startswith('image/svg'):
         mime_type = 'image/svg+xml'
 
+    if mime_type.startswith('text/'):
+        content_data = content_data.decode('utf-8', errors='replace')
+
     return {'content_data': content_data,
             'language': language,
             'mimetype': mime_type}
diff --git a/swh/web/tests/browse/views/test_content.py b/swh/web/tests/browse/views/test_content.py
--- a/swh/web/tests/browse/views/test_content.py
+++ b/swh/web/tests/browse/views/test_content.py
@@ -1,4 +1,4 @@
-# Copyright (C) 2017-2019  The Software Heritage developers
+# Copyright (C) 2017-2020  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU Affero General Public License version 3, or any later version
 # See top-level LICENSE file for more information
@@ -378,5 +378,9 @@
     mime_type, encoding, content_data = _re_encode_content(
         mime_type, encoding, content_data['data'])
 
-    return prepare_content_for_display(content_data, mime_type,
-                                       content['path'])
+    content_display = prepare_content_for_display(content_data, mime_type,
+                                                  content['path'])
+
+    assert type(content_display['content_data']) == str
+
+    return content_display
diff --git a/swh/web/tests/browse/views/test_origin.py b/swh/web/tests/browse/views/test_origin.py
--- a/swh/web/tests/browse/views/test_origin.py
+++ b/swh/web/tests/browse/views/test_origin.py
@@ -1,4 +1,4 @@
-# Copyright (C) 2017-2019  The Software Heritage developers
+# Copyright (C) 2017-2020  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU Affero General Public License version 3, or any later version
 # See top-level LICENSE file for more information
@@ -564,6 +564,8 @@
     assert resp.status_code == 200
     assert_template_used(resp, 'browse/content.html')
 
+    assert type(content['data']) == str
+
     assert_contains(resp, '<code class="%s">' %
                     content['hljs_language'])
     assert_contains(resp, escape(content['data']))
diff --git a/swh/web/tests/data.py b/swh/web/tests/data.py
--- a/swh/web/tests/data.py
+++ b/swh/web/tests/data.py
@@ -1,4 +1,4 @@
-# Copyright (C) 2018-2019  The Software Heritage developers
+# Copyright (C) 2018-2020  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU Affero General Public License version 3, or any later version
 # See top-level LICENSE file for more information
@@ -24,7 +24,8 @@
 from swh.storage.algos.dir_iterators import dir_iterator
 from swh.web import config
 from swh.web.browse.utils import (
-    get_mimetype_and_encoding_for_content, prepare_content_for_display
+    get_mimetype_and_encoding_for_content, prepare_content_for_display,
+    _re_encode_content
 )
 from swh.web.common import service
 from swh.web.common.highlightjs import get_hljs_language_from_filename
@@ -241,6 +242,8 @@
             cnt = next(storage.content_get([sha1]))
             mimetype, encoding = get_mimetype_and_encoding_for_content(
                 cnt['data'])
+            _, _, cnt['data'] = _re_encode_content(
+                mimetype, encoding, cnt['data'])
             content_display_data = prepare_content_for_display(
                 cnt['data'], mimetype, path)
             contents[-1]['path'] = path