diff --git a/lib/ruby_llm/schema/dsl.rb b/lib/ruby_llm/schema/dsl.rb
index 7c52745..d7b9489 100644
--- a/lib/ruby_llm/schema/dsl.rb
+++ b/lib/ruby_llm/schema/dsl.rb
@@ -81,7 +81,8 @@ def define(name, &)
         definitions[name] = {
           type: "object",
           properties: sub_schema.properties,
-          required: sub_schema.required_properties
+          required: sub_schema.required_properties,
+          additionalProperties: sub_schema.additional_properties
         }
       end
 
@@ -139,7 +140,7 @@ def build_property_schema(type, **options, &)
               type: "object",
               properties: sub_schema.properties,
               required: sub_schema.required_properties,
-              additionalProperties: additional_properties,
+              additionalProperties: sub_schema.additional_properties,
               description: options[:description]
             }.compact
           end
diff --git a/spec/ruby_llm/schema_spec.rb b/spec/ruby_llm/schema_spec.rb
index 4725b2a..19817e3 100644
--- a/spec/ruby_llm/schema_spec.rb
+++ b/spec/ruby_llm/schema_spec.rb
@@ -244,7 +244,8 @@
           street: {type: "string"},
           city: {type: "string"}
         },
-        required: %i[street city]
+        required: %i[street city],
+        additionalProperties: false
       })
     end
 
@@ -269,7 +270,8 @@
           street: {type: "string"},
           city: {type: "string"}
         },
-        required: %i[street city]
+        required: %i[street city],
+        additionalProperties: false
       })
     end
   end