diff --git a/chat.go b/chat.go
index fcaf79cf7..69bbc11d4 100644
--- a/chat.go
+++ b/chat.go
@@ -188,6 +188,7 @@ type FunctionCall struct {
 	Name string `json:"name,omitempty"`
 	// call function with arguments in JSON format
 	Arguments string `json:"arguments,omitempty"`
+	Output    string `json:"output,omitempty"`
 }
 
 type ChatCompletionResponseFormatType string
diff --git a/run_test.go b/run_test.go
index cdf99db05..7730d6652 100644
--- a/run_test.go
+++ b/run_test.go
@@ -52,6 +52,18 @@ func TestRun(t *testing.T) {
 							Object:    "run",
 							CreatedAt: 1234567890,
 							Status:    openai.RunStepStatusCompleted,
+							StepDetails: openai.StepDetails{
+								Type: openai.RunStepTypeToolCalls,
+								ToolCalls: []openai.ToolCall{
+									{
+										Function: openai.FunctionCall{
+											Name:      "test",
+											Arguments: "{}",
+											Output:    "test",
+										},
+									},
+								},
+							},
 						},
 					},
 				})