diff --git a/libresvip/core/compat.py b/libresvip/core/compat.py
index 7b71100d..a5f9fdcd 100644
--- a/libresvip/core/compat.py
+++ b/libresvip/core/compat.py
@@ -5,6 +5,10 @@
 except ImportError:
     import json
 
+    if hasattr(json, "_default_encoder"):
+        json._default_encoder.item_separator = ","
+        json._default_encoder.key_separator = ":"
+
 try:
     import pyzstd as zstd
 except ImportError: