diff --git a/bilby/core/utils/io.py b/bilby/core/utils/io.py
index 80590faf4ceb49b697ad0aa1747a2e1ba242cd2f..57a2cd2dde0f7195fde00ecc6941eb2151751d60 100644
--- a/bilby/core/utils/io.py
+++ b/bilby/core/utils/io.py
@@ -154,13 +154,16 @@ def decode_bilby_json(dct):
         try:
             cls = getattr(import_module(dct["__module__"]), dct["__name__"])
         except AttributeError:
-            logger.debug(
+            logger.warning(
                 "Unknown prior class for parameter {}, defaulting to base Prior object".format(
                     dct["kwargs"]["name"]
                 )
             )
             from ..prior import Prior
 
+            for key in list(dct["kwargs"].keys()):
+                if key not in ["name", "latex_label", "unit", "minimum", "maximum", "boundary"]:
+                    dct["kwargs"].pop(key)
             cls = Prior
         obj = cls(**dct["kwargs"])
         return obj