diff --git a/include/rapidjson/schema.h b/include/rapidjson/schema.h
index 2c5def1..cbcb550 100644
--- a/include/rapidjson/schema.h
+++ b/include/rapidjson/schema.h
@@ -410,9 +410,11 @@ public:
                 }
             }
 
-        AssignIfExist(allOf_, *schemaDocument, p, value, GetAllOfString(), document);
-        AssignIfExist(anyOf_, *schemaDocument, p, value, GetAnyOfString(), document);
-        AssignIfExist(oneOf_, *schemaDocument, p, value, GetOneOfString(), document);
+        if (schemaDocument) {
+            AssignIfExist(allOf_, *schemaDocument, p, value, GetAllOfString(), document);
+            AssignIfExist(anyOf_, *schemaDocument, p, value, GetAnyOfString(), document);
+            AssignIfExist(oneOf_, *schemaDocument, p, value, GetOneOfString(), document);
+        }
 
         if (const ValueType* v = GetMember(value, GetNotString())) {
             schemaDocument->CreateSchema(&not_, p.Append(GetNotString(), allocator_), *v, document);