diff --git a/src/core/definer.ts b/src/core/definer.ts
index 26d2041..813f1e4 100644
--- a/src/core/definer.ts
+++ b/src/core/definer.ts
@@ -130,11 +130,15 @@ function defineRoute<
   ];
 
   const responses = bundleResponses(input.responses);
-  const response400 = addBadRequest(input.queryParams, input.requestBody);
-  if (response400) {
-    responses["400"] = response400;
+  if (!input.responses["400"]) {
+    const response400 = addBadRequest(input.queryParams, input.requestBody);
+    if (response400) {
+      responses["400"] = response400;
+    }
+  }
+  if (!input.responses["500"]) {
+    responses["500"] = { description: "Internal Server Error" };
   }
-  responses["500"] = { description: "Internal Server Error" };
 
   handler.apiData = {
     operationId: input.operationId,