diff --git a/misc/scripts/models-as-data/bulk_generate_mad.py b/misc/scripts/models-as-data/bulk_generate_mad.py
index 7238f030c561..454df3741fa6 100755
--- a/misc/scripts/models-as-data/bulk_generate_mad.py
+++ b/misc/scripts/models-as-data/bulk_generate_mad.py
@@ -548,7 +548,7 @@ def main(config, args) -> None:
     parser.add_argument(
         "--extension-format",
         choices=["json", "yaml"],
-        default="yaml",
+        default="json",
         help="Format for the generated data extension files (default %(default)s)",
     )
     args = parser.parse_args()
diff --git a/misc/scripts/models-as-data/convert_extensions.py b/misc/scripts/models-as-data/convert_extensions.py
index 62ba64acf44e..381060646795 100644
--- a/misc/scripts/models-as-data/convert_extensions.py
+++ b/misc/scripts/models-as-data/convert_extensions.py
@@ -19,8 +19,8 @@ def __init__(self, language, dbDir):
         )
         self.extDir = os.path.join(self.codeQlRoot, f"{self.language}/ql/lib/ext/")
         self.dirname = "modelconverter"
-        # N.B. change this to .model.json to change the output format:
-        self.modelFileExtension = ".model.yml"
+        # N.B. change this to .model.yml to change the output format:
+        self.modelFileExtension = ".model.json"
         self.workDir = tempfile.mkdtemp()
 
     def runQuery(self, query):
diff --git a/misc/scripts/models-as-data/generate_mad.py b/misc/scripts/models-as-data/generate_mad.py
index 25b2fb9ae887..4e117d8ec315 100755
--- a/misc/scripts/models-as-data/generate_mad.py
+++ b/misc/scripts/models-as-data/generate_mad.py
@@ -33,7 +33,7 @@ class Generator:
     threads = 0
     folder = ""
     single_file = None
-    extension_format = "yaml"
+    extension_format = "json"
 
     def __init__(self, language=None):
         self.language = language
@@ -123,7 +123,7 @@ def make():
         p.add_argument(
             "--extension-format",
             choices=["json", "yaml"],
-            default="yaml",
+            default="json",
             help="Format for the generated data extension files (default %(default)s)",
         )
         generator = p.parse_args(namespace=Generator())