diff --git a/per-message-s3-exporter/main.py b/per-message-s3-exporter/main.py
index 8c2025f..8a16520 100644
--- a/per-message-s3-exporter/main.py
+++ b/per-message-s3-exporter/main.py
@@ -329,10 +329,11 @@ def _s3_bucket_folder(self) -> str:
 
     def _s3_file_extension(self) -> str:
         """File extension to use for uploads to S3"""
+        base_extension = ".json"
         if self.compression_type == "none":
-            return ""
+            return base_extension
 
-        return ".bz2"
+        return f"{base_extension}.bz2"
 
     def batch_filename(self) -> str:
         """Filename to use in S3 for writing out the Firehose messages"""