diff --git a/core/html.py b/core/html.py
index 3c48df4..c413cf4 100644
--- a/core/html.py
+++ b/core/html.py
@@ -139,8 +139,11 @@ class ContentRenderer:
                 url = str(mention.urls.view)
             else:
                 url = mention.absolute_profile_uri()
-            possible_matches[mention.username.lower()] = url
-            possible_matches[f"{mention.username.lower()}@{mention.domain_id}"] = url
+            # Might not have fetched it (yet)
+            if mention.username:
+                username = mention.username.lower()
+                possible_matches[username] = url
+                possible_matches[f"{username}@{mention.domain_id}"] = url
 
         collapse_name: dict[str, str] = {}
 
diff --git a/tests/core/test_html.py b/tests/core/test_html.py
index 5589105..fe7b098 100644
--- a/tests/core/test_html.py
+++ b/tests/core/test_html.py
@@ -75,15 +75,27 @@ def test_link_mixcase_mentions():
     fake_mention2.username = "manfre"
     fake_mention2.domain_id = "takahe.social"
     fake_mention2.urls.view = "https://takahe.social/@manfre@takahe.social/"
+
+    unfetched_mention = Mock()
+    unfetched_mention.username = None
+    unfetched_mention.domain_id = None
+    unfetched_mention.urls.view = "/None@None/"
+
     fake_post = Mock()
-    fake_post.mentions.all.return_value = [fake_mention, fake_mention2]
+    fake_post.mentions.all.return_value = [
+        fake_mention,
+        fake_mention2,
+        unfetched_mention,
+    ]
     fake_post.author.domain.uri_domain = "example.com"
     fake_post.emojis.all.return_value = []
 
-    assert (
-        renderer.render_post(
-            "@Manfre@manfre.net @mAnFrE@takahe.social @manfre@manfre.net",
-            fake_post,
-        )
-        == '<a href="/@Manfre@manfre.net/">@Manfre</a> <a href="https://takahe.social/@manfre@takahe.social/">@mAnFrE@takahe.social</a> <a href="/@Manfre@manfre.net/">@manfre</a>'
+    assert renderer.render_post(
+        "@Manfre@manfre.net @mAnFrE@takahe.social @manfre@manfre.net @unfetched@manfre.net",
+        fake_post,
+    ) == (
+        '<a href="/@Manfre@manfre.net/">@Manfre</a> '
+        '<a href="https://takahe.social/@manfre@takahe.social/">@mAnFrE@takahe.social</a> '
+        '<a href="/@Manfre@manfre.net/">@manfre</a> '
+        "@unfetched@manfre.net"
     )