diff --git a/llama_cpp/llama_grammar.py b/llama_cpp/llama_grammar.py
index d8ef563..3eb3b96 100644
--- a/llama_cpp/llama_grammar.py
+++ b/llama_cpp/llama_grammar.py
@@ -1471,12 +1471,15 @@ class SchemaConverter:
 
         if schema_type == "object" and "properties" in schema:
             # TODO: `required` keyword
-            prop_order = self._prop_order
-            prop_pairs = sorted(
-                schema["properties"].items(),
-                # sort by position in prop_order (if specified) then by key
-                key=lambda kv: (prop_order.get(kv[0], len(prop_order)), kv[0]),
-            )
+            if self._prop_order:
+                prop_order = self._prop_order
+                prop_pairs = sorted(
+                    schema["properties"].items(),
+                    # sort by position in prop_order (if specified) then by key
+                    key=lambda kv: (prop_order.get(kv[0], len(prop_order)), kv[0]),
+                )
+            else:
+                prop_pairs = schema["properties"].items()
 
             rule = '"{" space'
             for i, (prop_name, prop_schema) in enumerate(prop_pairs):