diff --git a/app/utils/emoji.py b/app/utils/emoji.py
index 0fcf6bc..e533bae 100644
--- a/app/utils/emoji.py
+++ b/app/utils/emoji.py
@@ -23,6 +23,8 @@ def _load_emojis(root_dir: Path, base_url: str) -> None:
             mt = mimetypes.guess_type(emoji.name)[0]
             if mt and mt.startswith("image/"):
                 name = emoji.name.split(".")[0]
+                if not re.match(EMOJI_REGEX, f':{name}:'):
+                    continue
                 ap_emoji: "RawObject" = {
                     "type": "Emoji",
                     "name": f":{name}:",
diff --git a/docs/user_guide.md b/docs/user_guide.md
index 96d9836..ec398f3 100644
--- a/docs/user_guide.md
+++ b/docs/user_guide.md
@@ -113,6 +113,7 @@ You can copy/paste them from [getemoji.com](https://getemoji.com/).
 #### Custom emoji
 
 You can add custom emoji in the `data/custom_emoji` directory and they will be picked automatically.
+Do not use exotic characters in filename - only letters, numbers, and underscore symbol `_` are allowed.
 
 #### Custom CSS