diff --git a/swh/web/api/utils.py b/swh/web/api/utils.py
--- a/swh/web/api/utils.py
+++ b/swh/web/api/utils.py
@@ -238,7 +238,7 @@
             )
         revision["children_urls"] = children
 
-    if "message_decoding_failed" in revision:
+    if "decoding_failures" in revision and "message" in revision["decoding_failures"]:
         revision["message_url"] = reverse(
             "api-1-revision-raw-message",
             url_args={"sha1_git": revision["id"]},
diff --git a/swh/web/common/converters.py b/swh/web/common/converters.py
--- a/swh/web/common/converters.py
+++ b/swh/web/common/converters.py
@@ -279,7 +279,7 @@
     revision_d = from_swh(
         revision_d,
         hashess={"id", "directory", "parents", "children"},
-        bytess={"name", "fullname", "email", "extra_headers"},
+        bytess={"name", "fullname", "email", "extra_headers", "message"},
         convert={"metadata"},
         convert_fn=convert_revision_metadata,
         dates={"date", "committer_date"},
@@ -288,12 +288,6 @@
     if revision_d:
         if "parents" in revision_d:
             revision_d["merge"] = len(revision_d["parents"]) > 1
-        if "message" in revision_d:
-            try:
-                revision_d["message"] = revision_d["message"].decode("utf-8")
-            except UnicodeDecodeError:
-                revision_d["message_decoding_failed"] = True
-                revision_d["message"] = None
 
     return revision_d
 
diff --git a/swh/web/templates/includes/apidoc-header.html b/swh/web/templates/includes/apidoc-header.html
--- a/swh/web/templates/includes/apidoc-header.html
+++ b/swh/web/templates/includes/apidoc-header.html
@@ -155,6 +155,17 @@
 </ul>
 <p>Unavailability of the underlying storage backend will result in a
   <code>503 Service Unavailable</code> HTTP response.</p>
+<h4 id="utf8-decoding-errors">UTF-8 decoding errors</h4>
+<p>While attempting to decode UTF-8 strings from raw bytes stored in the archive, some errors
+might happen when generating an API response. In that case, an extra field <code>decoding_failures</code>
+will be added to each concerned JSON object (possibly nested). It will contain the list of its key
+names where UTF-8 decoding failed.
+</p>
+<p>
+A string that could not be decoded will have the bytes of its invalid UTF-8 sequences escaped as
+<code>\\x&lt;hex value&gt;</code>.
+</p>
+</h4>
 <h4 id="pagination">Pagination</h4>
 <p>Requests that might potentially return many items will be paginated.</p>
 <p>Page size is set to a default (usually: 10 items), but might be overridden with the
diff --git a/swh/web/tests/api/test_utils.py b/swh/web/tests/api/test_utils.py
--- a/swh/web/tests/api/test_utils.py
+++ b/swh/web/tests/api/test_utils.py
@@ -471,8 +471,7 @@
 ):
 
     revision_data = archive_data.revision_get(revision)
-    revision_data["message"] = None
-    revision_data["message_decoding_failed"] = (True,)
+    revision_data["decoding_failures"] = ["message"]
     revision_data["parents"] = revision_data["parents"] + (parent_revision,)
     revision_data["children"] = child_revision
 
diff --git a/swh/web/tests/common/test_converters.py b/swh/web/tests/common/test_converters.py
--- a/swh/web/tests/common/test_converters.py
+++ b/swh/web/tests/common/test_converters.py
@@ -608,8 +608,8 @@
             "fullname": "robot robot@softwareheritage.org",
             "email": "robot@softwareheritage.org",
         },
-        "message": None,
-        "message_decoding_failed": True,
+        "message": "invalid message \\xff",
+        "decoding_failures": ["message"],
         "date": "2000-01-17T11:23:54+00:00",
         "committer_date": "2000-01-17T11:23:54+00:00",
         "children": ["123546353ed3480476f032475e7c244eff7371d5"],
diff --git a/swh/web/tests/common/test_service.py b/swh/web/tests/common/test_service.py
--- a/swh/web/tests/common/test_service.py
+++ b/swh/web/tests/common/test_service.py
@@ -522,8 +522,8 @@
     archive_data.revision_add([Revision.from_dict(new_revision)])
 
     revision = service.lookup_revision(hash_to_hex(new_revision["id"]))
-    assert revision["message"] is None
-    assert revision["message_decoding_failed"] is True
+    assert revision["message"] == "elegant fix for bug \\xff"
+    assert revision["decoding_failures"] == ["message"]
 
 
 @given(new_revision())