diff --git a/optuna_dashboard/ts/apiClient.ts b/optuna_dashboard/ts/apiClient.ts
index b03f5691..12feaf4a 100644
--- a/optuna_dashboard/ts/apiClient.ts
+++ b/optuna_dashboard/ts/apiClient.ts
@@ -30,7 +30,7 @@ interface TrialResponse {
   system_attrs: Attribute[]
   note: Note
   artifacts: Artifact[]
-  constraints?: number[]
+  constraints: number[]
 }
 
 const convertTrialResponse = (res: TrialResponse): Trial => {
diff --git a/optuna_dashboard/ts/types/index.d.ts b/optuna_dashboard/ts/types/index.d.ts
index c49339e0..040a1fc3 100644
--- a/optuna_dashboard/ts/types/index.d.ts
+++ b/optuna_dashboard/ts/types/index.d.ts
@@ -112,7 +112,7 @@ type Trial = {
   }[]
   user_attrs: Attribute[]
   system_attrs: Attribute[]
-  constraints?: number[]
+  constraints: number[]
   note: Note
   artifacts: Artifact[]
 }