diff --git a/internal/runtime/executor/codex_executor.go b/internal/runtime/executor/codex_executor.go
index 273987ea..0abec8af 100644
--- a/internal/runtime/executor/codex_executor.go
+++ b/internal/runtime/executor/codex_executor.go
@@ -106,6 +106,9 @@ func (e *CodexExecutor) Execute(ctx context.Context, auth *cliproxyauth.Auth, re
 	body, _ = sjson.SetBytes(body, "stream", true)
 	body, _ = sjson.DeleteBytes(body, "previous_response_id")
 	body, _ = sjson.DeleteBytes(body, "prompt_cache_retention")
+	if !gjson.GetBytes(body, "instructions").Exists() {
+		body, _ = sjson.SetBytes(body, "instructions", "")
+	}
 
 	url := strings.TrimSuffix(baseURL, "/") + "/responses"
 	httpReq, err := e.cacheHelper(ctx, from, url, req, body)
@@ -213,6 +216,9 @@ func (e *CodexExecutor) ExecuteStream(ctx context.Context, auth *cliproxyauth.Au
 	body, _ = sjson.DeleteBytes(body, "previous_response_id")
 	body, _ = sjson.DeleteBytes(body, "prompt_cache_retention")
 	body, _ = sjson.SetBytes(body, "model", baseModel)
+	if !gjson.GetBytes(body, "instructions").Exists() {
+		body, _ = sjson.SetBytes(body, "instructions", "")
+	}
 
 	url := strings.TrimSuffix(baseURL, "/") + "/responses"
 	httpReq, err := e.cacheHelper(ctx, from, url, req, body)
@@ -317,6 +323,9 @@ func (e *CodexExecutor) CountTokens(ctx context.Context, auth *cliproxyauth.Auth
 	body, _ = sjson.DeleteBytes(body, "previous_response_id")
 	body, _ = sjson.DeleteBytes(body, "prompt_cache_retention")
 	body, _ = sjson.SetBytes(body, "stream", false)
+	if !gjson.GetBytes(body, "instructions").Exists() {
+		body, _ = sjson.SetBytes(body, "instructions", "")
+	}
 
 	enc, err := tokenizerForCodexModel(baseModel)
 	if err != nil {