diff --git a/app/schemas/eml.py b/app/schemas/eml.py
index bff9c07..0df7206 100644
--- a/app/schemas/eml.py
+++ b/app/schemas/eml.py
@@ -15,7 +15,7 @@ class Attachment(APIModel):
     raw: str
     filename: str
     size: int
-    extension: str
+    extension: Optional[str]
     hash_: Hash
     mime_type: str
     mime_type_short: str
diff --git a/frontend/src/types.ts b/frontend/src/types.ts
index 049060a..f8b3807 100644
--- a/frontend/src/types.ts
+++ b/frontend/src/types.ts
@@ -21,7 +21,7 @@ interface Dictionary {
 export interface Attachment {
   filename: string;
   size: number;
-  extension: string;
+  extension: string | undefined;
   hash: Hash;
   mimeType: string;
   mimeTypeShort: string;