diff --git a/signal-server-openapi.yaml b/signal-server-openapi.yaml
index 30ecbf11d..cffc09704 100644
--- a/signal-server-openapi.yaml
+++ b/signal-server-openapi.yaml
@@ -508,8 +508,10 @@ paths:
       tags:
       - Archive
       summary: Fetch message backup upload form
-      description: Retrieve an upload form that can be used to perform a resumable
-        upload of a message backup.
+      description: |
+        Retrieve an upload form that can be used to perform a resumable upload of a message backup.
+
+        Uploads with the returned form will be limited to a maximum size of the provided uploadLength.
       operationId: backup
       parameters:
       - name: User-Agent
@@ -1248,7 +1250,8 @@ paths:
         Retrieve an upload form that can be used to perform a resumable upload of an attachment. After uploading, the
         attachment can be copied into the backup at PUT /archives/media/.
 
-        Like the account authenticated version at /attachments, the uploaded object is only temporary.
+        Like the account authenticated version at /attachments, the uploaded object is only temporary. Uploads with
+        the returned form will be limited to a maximum size of the provided uploadLength.
       operationId: uploadTemporaryAttachment
       parameters:
       - name: User-Agent
@@ -1269,6 +1272,12 @@ paths:
         required: true
         schema:
           type: string
+      - name: uploadLength
+        in: query
+        description: The size of the temporary attachment to upload in bytes
+        schema:
+          type: integer
+          format: int64
       responses:
         "200":
           content:
@@ -1277,6 +1286,10 @@ paths:
                 $ref: "#/components/schemas/UploadDescriptorResponse"
         "429":
           description: Rate limited.
+        "413":
+          description: The provided uploadLength is larger than the maximum supported
+            upload size. The maximum upload size is subject to change and is governed
+            by `global.attachments.maxBytes`.
         "403":
           description: Forbidden. The request had insufficient permissions to perform
             the requested action
@@ -1300,7 +1313,16 @@ paths:
       description: |
         Retrieve an upload form that can be used to perform a resumable upload. The response will include a cdn number
         indicating what protocol should be used to perform the upload.
+
+        Uploads with the returned form will be limited to a maximum size of the provided uploadLength.
       operationId: getAttachmentUploadForm
+      parameters:
+      - name: uploadLength
+        in: query
+        description: The size of the attachment to upload in bytes
+        schema:
+          type: integer
+          format: int64
       responses:
         "200":
           description: "Success, response body includes upload form"
@@ -1308,6 +1330,12 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/AttachmentDescriptorV3"
+        "400":
+          description: The provided uploadLength was not valid
+        "413":
+          description: The provided uploadLength is larger than the maximum supported
+            upload size. The maximum upload size is subject to change and is governed
+            by `global.attachments.maxBytes`.
         "429":
           description: Too many attempts
           headers: