diff --git a/s4/clients/local.py b/s4/clients/local.py
index 10244a4..f919340 100644
--- a/s4/clients/local.py
+++ b/s4/clients/local.py
@@ -148,7 +148,7 @@ def _load_index(self):
             return {}
 
         content_type = magic.from_file(index_path, mime=True)
-        if content_type == "text/plain":
+        if content_type in ("application/json", "text/plain"):
             logger.debug("Detected plaintext encoding for reading index")
             method = open
         elif content_type in ("application/gzip", "application/x-gzip"):
diff --git a/s4/clients/s3.py b/s4/clients/s3.py
index 06a9ff3..aec05e7 100644
--- a/s4/clients/s3.py
+++ b/s4/clients/s3.py
@@ -132,7 +132,7 @@ def load_index(self):
             body = resp["Body"].read()
             content_type = magic.from_buffer(body, mime=True)
 
-            if content_type == "text/plain":
+            if content_type in ("application/json", "text/plain"):
                 logger.debug("Detected plain text encoding for index")
                 return json.loads(body.decode("utf-8"))