diff --git a/app/__init__.py b/app/__init__.py
index a708553..45c41a3 100644
--- a/app/__init__.py
+++ b/app/__init__.py
@@ -51,21 +51,26 @@ class _ChunkedTransferMiddleware:
         self.app = app
 
     def __call__(self, environ, start_response):
-        has_content_length = environ.get("CONTENT_LENGTH")
-        if not has_content_length and environ.get("REQUEST_METHOD") in ("PUT", "POST"):
-            transfer_chunked = "chunked" in environ.get("HTTP_TRANSFER_ENCODING", "").lower()
-            has_body_hint = bool(environ.get("HTTP_X_AMZ_DECODED_CONTENT_LENGTH"))
-            content_encoding = environ.get("HTTP_CONTENT_ENCODING", "")
-            has_aws_chunked = "aws-chunked" in content_encoding.lower()
-            if transfer_chunked or has_body_hint or has_aws_chunked:
-                try:
-                    raw = environ["wsgi.input"]
-                    body = raw.read()
-                except Exception:
-                    body = b""
-                if body:
-                    environ["wsgi.input"] = io.BytesIO(body)
-                    environ["CONTENT_LENGTH"] = str(len(body))
+        if environ.get("REQUEST_METHOD") not in ("PUT", "POST"):
+            return self.app(environ, start_response)
+
+        content_length = environ.get("CONTENT_LENGTH")
+        body_expected = (
+            environ.get("HTTP_X_AMZ_DECODED_CONTENT_LENGTH")
+            or "chunked" in environ.get("HTTP_TRANSFER_ENCODING", "").lower()
+            or "aws-chunked" in environ.get("HTTP_CONTENT_ENCODING", "").lower()
+        )
+
+        if body_expected and (not content_length or content_length == "0"):
+            try:
+                raw = environ["wsgi.input"]
+                body = raw.read()
+            except Exception:
+                body = b""
+            if body:
+                environ["wsgi.input"] = io.BytesIO(body)
+                environ["CONTENT_LENGTH"] = str(len(body))
+
         return self.app(environ, start_response)