diff --git a/app/utils.py b/app/utils.py
index b0ce047..d72386d 100644
--- a/app/utils.py
+++ b/app/utils.py
@@ -58,9 +58,6 @@ def document_s3_key(org_id: str, document_id: str, filename: str) -> str:
     return f"{s3_path_prefix(org_id, document_id)}{filename}"
 
 def sanitize_filename(filename: str) -> str:
-    """Sanitize filename for S3"""
-    # Remove path separators and special characters
-    filename = filename.replace("/", "_").replace("\\", "_")
-    # Keep only safe characters
-    safe_chars = set("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789.-_")
-    return "".join(c for c in filename if c in safe_chars)
+    """URL encode filename for S3"""
+    from urllib.parse import quote
+    return quote(filename, safe="")