diff --git a/packages/backend/src/server/api/openapi/gen-spec.ts b/packages/backend/src/server/api/openapi/gen-spec.ts
index 7679a9b464..2a14270a24 100644
--- a/packages/backend/src/server/api/openapi/gen-spec.ts
+++ b/packages/backend/src/server/api/openapi/gen-spec.ts
@@ -93,7 +93,7 @@ export function genOpenapiSpec(config: Config, includeSelfRef = false) {
 		const hasBody = (schema.type === 'object' && schema.properties && Object.keys(schema.properties).length >= 1);
 
 		const info = {
-			operationId: endpoint.name,
+			operationId: endpoint.name.replaceAll('/', '___'), // NOTE: スラッシュは使えない
 			summary: endpoint.name,
 			description: desc,
 			externalDocs: {