diff --git a/moto/moto_proxy/utils.py b/moto/moto_proxy/utils.py
index bbdb055af..bcd7fe299 100644
--- a/moto/moto_proxy/utils.py
+++ b/moto/moto_proxy/utils.py
@@ -8,8 +8,8 @@ def get_body_from_form_data(
     body: bytes, boundary: str
 ) -> Tuple[Optional[bytes], Dict[str, str]]:
     body_stream = io.BytesIO(body)
-    parser = multipart.MultipartParser(body_stream, boundary=boundary)
-
+    parser = multipart.MultipartParser(boundary=boundary)
+    parser.write(body_stream)
     data = None
     headers: Dict[str, str] = {}
     for prt in parser.parts():