diff --git a/common/json-schema-to-grammar.cpp b/common/json-schema-to-grammar.cpp
index 737bae27c..58f3c2ae9 100644
--- a/common/json-schema-to-grammar.cpp
+++ b/common/json-schema-to-grammar.cpp
@@ -625,7 +625,7 @@ public:
             return _add_rule(rule_name,
                 _build_object_rule(
                     properties, required, name,
-                    schema.contains("additionalProperties") ? schema["additionalProperties"] : json()));
+                    schema.contains("additionalProperties") ? schema["additionalProperties"] : json::object()));
         } else if ((schema_type.is_null() || schema_type == "object") && schema.contains("allOf")) {
             std::unordered_set<std::string> required;
             std::vector<std::pair<std::string, json>> properties;
diff --git a/examples/json_schema_to_grammar.py b/examples/json_schema_to_grammar.py
index 7d889c3fe..15631d53c 100755
--- a/examples/json_schema_to_grammar.py
+++ b/examples/json_schema_to_grammar.py
@@ -372,7 +372,10 @@ class SchemaConverter:
               ('additionalProperties' in schema and schema['additionalProperties'] is not True)):
             required = set(schema.get('required', []))
             properties = list(schema.get('properties', {}).items())
-            return self._add_rule(rule_name, self._build_object_rule(properties, required, name, schema.get('additionalProperties')))
+            additional_properties = schema.get('additionalProperties', True)
+            if additional_properties is None:
+                additional_properties = True
+            return self._add_rule(rule_name, self._build_object_rule(properties, required, name, additional_properties))
 
         elif schema_type in (None, 'object') and 'allOf' in schema:
             required = set()
diff --git a/examples/server/public/json-schema-to-grammar.mjs b/examples/server/public/json-schema-to-grammar.mjs
index cef11eab8..ded37c981 100644
--- a/examples/server/public/json-schema-to-grammar.mjs
+++ b/examples/server/public/json-schema-to-grammar.mjs
@@ -374,7 +374,11 @@ export class SchemaConverter {
                 ('additionalProperties' in schema && schema.additionalProperties !== true))) {
       const required = new Set(schema.required || []);
       const properties = Object.entries(schema.properties ?? {});
-      return this._addRule(ruleName, this._buildObjectRule(properties, required, name, schema.additionalProperties));
+      let additionalProperties = schema.additionalProperties;
+      if (additionalProperties === undefined) {
+        additionalProperties = true;
+      }
+      return this._addRule(ruleName, this._buildObjectRule(properties, required, name, additionalProperties));
     } else if ((schemaType === undefined || schemaType === 'object') && 'allOf' in schema) {
       const required = new Set();
       const properties = [];
diff --git a/tests/test-json-schema-to-grammar.cpp b/tests/test-json-schema-to-grammar.cpp
index 052c08073..780e1932a 100755
--- a/tests/test-json-schema-to-grammar.cpp
+++ b/tests/test-json-schema-to-grammar.cpp
@@ -751,15 +751,31 @@ static void test_all(const std::string & lang, std::function<void(const TestCase
         R"""(
             alternative-0 ::= foo
             alternative-1 ::= bar
-            bar ::= "{" space  (bar-b-kv )? "}" space
+            array ::= "[" space ( value ("," space value)* )? "]" space
+            bar ::= "{" space  (bar-b-kv bar-b-rest | bar-additional-kvs )? "}" space
+            bar-additional-kv ::= string ":" space bar-additional-value
+            bar-additional-kvs ::= bar-additional-kv ( "," space bar-additional-kv )*
+            bar-additional-value ::= object
             bar-b-kv ::= "\"b\"" space ":" space number
+            bar-b-rest ::= bar-additional-kvs
+            boolean ::= ("true" | "false") space
+            char ::= [^"\\] | "\\" (["\\/bfnrt] | "u" [0-9a-fA-F]{4})
             decimal-part ::= [0-9]{1,16}
-            foo ::= "{" space  (foo-a-kv )? "}" space
+            foo ::= "{" space  (foo-a-kv foo-a-rest | foo-additional-kvs )? "}" space
             foo-a-kv ::= "\"a\"" space ":" space number
+            foo-a-rest ::= foo-additional-kvs
+            foo-additional-kv ::= string ":" space foo-additional-value
+            foo-additional-kvs ::= foo-additional-kv ( "," space foo-additional-kv )*
+            foo-additional-value ::= object
             integral-part ::= [0] | [1-9] [0-9]{0,15}
+            null ::= "null" space
             number ::= ("-"? integral-part) ("." decimal-part)? ([eE] [-+]? integral-part)? space
+            object ::= "{" space ( string ":" space value ("," space string ":" space value)* )? "}" space
             root ::= alternative-0 | alternative-1
             space ::= " "?
+            string ::= "\"" char* "\"" space
+            value ::= object | array | string | number | boolean | null
+
         )"""
     });