diff --git a/mangum/__init__.py b/mangum/__init__.py
index f8090ec3..6364b08a 100644
--- a/mangum/__init__.py
+++ b/mangum/__init__.py
@@ -72,11 +72,10 @@ def on_response_start(self, headers: dict, status_code: int) -> None:
         self.response["headers"] = {k.decode(): v.decode() for k, v in headers.items()}
 
     def on_response_close(self) -> None:
+        body = self.body
         if self.binary:
-            body = base64.b64encode(self.body)
-        else:
-            body = self.body.decode()
-        self.response["body"] = body
+            body = base64.b64encode(body)
+        self.response["body"] = body.decode()
 
 
 class Mangum:
@@ -131,16 +130,12 @@ def asgi(self, event: dict, context: dict) -> dict:
         }
 
         binary = event.get("isBase64Encoded", False)
-        body = event["body"]
-
-        if body:
-            if binary:
-                body = base64.b64decode(body)
+        body = event["body"] or b""
 
-            else:
-                body = body.encode()
-        else:
-            body = b""
+        if binary:
+            body = base64.b64decode(body)
+        elif not isinstance(body, bytes):
+            body = body.encode()
 
         response = ASGICycle(scope, binary=binary)(self.app, body=body)
         return response
diff --git a/tests/test_aws.py b/tests/test_aws.py
index 894bdcd0..446b5af8 100644
--- a/tests/test_aws.py
+++ b/tests/test_aws.py
@@ -100,7 +100,7 @@ async def asgi(receive, send):
         "statusCode": 200,
         "isBase64Encoded": True,
         "headers": {"content-length": "3", "content-type": "text/plain; charset=utf-8"},
-        "body": body_encoded,
+        "body": body_encoded.decode(),
     }