diff --git a/sdk/api/handlers/openai/openai_responses_handlers.go b/sdk/api/handlers/openai/openai_responses_handlers.go
index 67c648dcf..578977d62 100644
--- a/sdk/api/handlers/openai/openai_responses_handlers.go
+++ b/sdk/api/handlers/openai/openai_responses_handlers.go
@@ -46,9 +46,10 @@ func writeResponsesSSEChunk(w io.Writer, chunk []byte) {
 }
 
 type responsesSSEFramer struct {
-	pending     []byte
-	outputItems map[int][]byte
-	outputOrder []int
+	pending              []byte
+	outputItems          map[int][]byte
+	outputOrder          []int
+	unindexedOutputItems [][]byte
 }
 
 func (f *responsesSSEFramer) WriteChunk(w io.Writer, chunk []byte) {
@@ -159,21 +160,23 @@ func (f *responsesSSEFramer) recordOutputItem(payload []byte) {
 		return
 	}
 
-	index := len(f.outputOrder)
 	if outputIndex := gjson.GetBytes(payload, "output_index"); outputIndex.Exists() {
-		index = int(outputIndex.Int())
+		index := int(outputIndex.Int())
+		if f.outputItems == nil {
+			f.outputItems = make(map[int][]byte)
+		}
+		if _, exists := f.outputItems[index]; !exists {
+			f.outputOrder = append(f.outputOrder, index)
+		}
+		f.outputItems[index] = append([]byte(nil), item.Raw...)
+		return
 	}
-	if f.outputItems == nil {
-		f.outputItems = make(map[int][]byte)
-	}
-	if _, exists := f.outputItems[index]; !exists {
-		f.outputOrder = append(f.outputOrder, index)
-	}
-	f.outputItems[index] = append([]byte(nil), item.Raw...)
+
+	f.unindexedOutputItems = append(f.unindexedOutputItems, append([]byte(nil), item.Raw...))
 }
 
 func (f *responsesSSEFramer) repairCompletedPayload(payload []byte) []byte {
-	if len(f.outputOrder) == 0 {
+	if len(f.outputOrder) == 0 && len(f.unindexedOutputItems) == 0 {
 		return payload
 	}
 	output := gjson.GetBytes(payload, "response.output")
@@ -197,6 +200,13 @@ func (f *responsesSSEFramer) repairCompletedPayload(payload []byte) []byte {
 		outputJSON.Write(item)
 		written++
 	}
+	for _, item := range f.unindexedOutputItems {
+		if written > 0 {
+			outputJSON.WriteByte(',')
+		}
+		outputJSON.Write(item)
+		written++
+	}
 	outputJSON.WriteByte(']')
 
 	repaired, err := sjson.SetRawBytes(payload, "response.output", outputJSON.Bytes())
diff --git a/sdk/api/handlers/openai/openai_responses_handlers_stream_test.go b/sdk/api/handlers/openai/openai_responses_handlers_stream_test.go
index 8b3f79e33..3851278fb 100644
--- a/sdk/api/handlers/openai/openai_responses_handlers_stream_test.go
+++ b/sdk/api/handlers/openai/openai_responses_handlers_stream_test.go
@@ -91,6 +91,37 @@ func TestForwardResponsesStreamRepairsEmptyCompletedOutputFromDoneItems(t *testi
 	}
 }
 
+func TestForwardResponsesStreamRepairsMixedIndexedAndUnindexedDoneItems(t *testing.T) {
+	h, recorder, c, flusher := newResponsesStreamTestHandler(t)
+
+	data := make(chan []byte, 3)
+	errs := make(chan *interfaces.ErrorMessage)
+	data <- []byte(`data: {"type":"response.output_item.done","output_index":1,"item":{"type":"function_call","id":"fc-1","call_id":"call-1","name":"shell","arguments":"{}","status":"completed"}}`)
+	data <- []byte(`data: {"type":"response.output_item.done","item":{"type":"message","id":"msg-1","role":"assistant","content":[{"type":"output_text","text":"done"}]}}`)
+	data <- []byte(`data: {"type":"response.completed","response":{"id":"resp-1","output":[]}}`)
+	close(data)
+	close(errs)
+
+	h.forwardResponsesStream(c, flusher, func(error) {}, data, errs, nil)
+
+	parts := strings.Split(strings.TrimSpace(recorder.Body.String()), "\n\n")
+	if len(parts) != 3 {
+		t.Fatalf("expected 3 SSE events, got %d. Body: %q", len(parts), recorder.Body.String())
+	}
+
+	payload := strings.TrimPrefix(parts[2], "data: ")
+	output := gjson.Get(payload, "response.output")
+	if !output.IsArray() || len(output.Array()) != 2 {
+		t.Fatalf("expected repaired completed output with 2 items, got %s", output.Raw)
+	}
+	if got := gjson.Get(payload, "response.output.0.name").String(); got != "shell" {
+		t.Fatalf("expected indexed function_call to be preserved first, got %q in %s", got, payload)
+	}
+	if got := gjson.Get(payload, "response.output.1.id").String(); got != "msg-1" {
+		t.Fatalf("expected unindexed message to be appended, got %q in %s", got, payload)
+	}
+}
+
 func TestForwardResponsesStreamReassemblesSplitSSEEventChunks(t *testing.T) {
 	h, recorder, c, flusher := newResponsesStreamTestHandler(t)