diff --git a/crates/goose-providers/src/formats/openai.rs b/crates/goose-providers/src/formats/openai.rs
index 912622bf0bf0..4c4e8acc9ff4 100644
--- a/crates/goose-providers/src/formats/openai.rs
+++ b/crates/goose-providers/src/formats/openai.rs
@@ -1004,8 +1004,9 @@ where
                 let mut tool_call_data: ToolCallData = HashMap::new();
 
                 if let Some(tool_calls) = &chunk.choices[0].delta.tool_calls {
-                    for tool_call in tool_calls {
-                        if let (Some(index), Some(id), Some(name)) = (tool_call.index, &tool_call.id, &tool_call.function.name) {
+                    for (position, tool_call) in tool_calls.iter().enumerate() {
+                        if let (Some(id), Some(name)) = (&tool_call.id, &tool_call.function.name) {
+                            let index = tool_call.index.unwrap_or(position as i32);
                             tool_call_data.insert(index, (id.clone(), name.clone(), tool_call.function.arguments.clone(), tool_call.extra.clone()));
                         }
                     }
@@ -3652,6 +3653,66 @@ data: [DONE]"#;
         Ok(())
     }
 
+    #[tokio::test]
+    async fn test_streaming_tool_call_without_tool_call_index() -> anyhow::Result<()> {
+        let response_lines = concat!(
+            "data: {\"id\":\"x\",\"object\":\"chat.completion.chunk\",\"model\":\"m\",\"choices\":[{\"index\":0,\"delta\":{\"role\":\"assistant\",\"tool_calls\":[{\"id\":\"functions.get_weather:0\",\"type\":\"function\",\"function\":{\"name\":\"get_weather\",\"arguments\":\"{\\\"city\\\": \\\"Paris\\\"}\"}}]},\"finish_reason\":\"tool_calls\"}]}\n",
+            "data: [DONE]"
+        );
+        let lines: Vec<String> = response_lines.lines().map(|s| s.to_string()).collect();
+        let response_stream = tokio_stream::iter(lines.into_iter().map(Ok));
+        let mut messages = std::pin::pin!(response_to_streaming_message(response_stream));
+
+        let mut tool_calls = Vec::new();
+        while let Some(result) = messages.next().await {
+            let (message, _usage) = result?;
+            if let Some(msg) = message {
+                for content in &msg.content {
+                    if let MessageContent::ToolRequest(request) = content {
+                        let tool_call = request.tool_call.as_ref().expect("tool call should parse");
+                        tool_calls.push((tool_call.name.to_string(), tool_call.arguments.clone()));
+                    }
+                }
+            }
+        }
+
+        assert_eq!(tool_calls.len(), 1);
+        assert_eq!(tool_calls[0].0, "get_weather");
+        assert_eq!(tool_calls[0].1, Some(object!({"city": "Paris"})));
+        Ok(())
+    }
+
+    #[tokio::test]
+    async fn test_streaming_multiple_tool_calls_without_tool_call_index() -> anyhow::Result<()> {
+        let response_lines = concat!(
+            "data: {\"id\":\"x\",\"object\":\"chat.completion.chunk\",\"model\":\"m\",\"choices\":[{\"index\":0,\"delta\":{\"role\":\"assistant\",\"tool_calls\":[{\"id\":\"functions.get_weather:0\",\"type\":\"function\",\"function\":{\"name\":\"get_weather\",\"arguments\":\"{\\\"city\\\": \\\"Paris\\\"}\"}},{\"id\":\"functions.get_weather:1\",\"type\":\"function\",\"function\":{\"name\":\"get_weather\",\"arguments\":\"{\\\"city\\\": \\\"Tokyo\\\"}\"}}]},\"finish_reason\":\"tool_calls\"}]}\n",
+            "data: [DONE]"
+        );
+        let lines: Vec<String> = response_lines.lines().map(|s| s.to_string()).collect();
+        let response_stream = tokio_stream::iter(lines.into_iter().map(Ok));
+        let mut messages = std::pin::pin!(response_to_streaming_message(response_stream));
+
+        let mut tool_calls = Vec::new();
+        while let Some(result) = messages.next().await {
+            let (message, _usage) = result?;
+            if let Some(msg) = message {
+                for content in &msg.content {
+                    if let MessageContent::ToolRequest(request) = content {
+                        let tool_call = request.tool_call.as_ref().expect("tool call should parse");
+                        tool_calls.push((tool_call.name.to_string(), tool_call.arguments.clone()));
+                    }
+                }
+            }
+        }
+
+        assert_eq!(tool_calls.len(), 2);
+        assert_eq!(tool_calls[0].0, "get_weather");
+        assert_eq!(tool_calls[0].1, Some(object!({"city": "Paris"})));
+        assert_eq!(tool_calls[1].0, "get_weather");
+        assert_eq!(tool_calls[1].1, Some(object!({"city": "Tokyo"})));
+        Ok(())
+    }
+
     // Streaming counterpart: both fields in one delta must parse and yield
     // thinking content, not fail with "duplicate field `reasoning_content`".
     #[tokio::test]