diff --git a/src/main/kotlin/conversation/ConversationEngine.kt b/src/main/kotlin/conversation/ConversationEngine.kt
index 1646e4c..e720cbe 100644
--- a/src/main/kotlin/conversation/ConversationEngine.kt
+++ b/src/main/kotlin/conversation/ConversationEngine.kt
@@ -5,6 +5,7 @@ import com.aallam.openai.api.chat.ChatCompletionRequest
 import com.aallam.openai.api.chat.ChatMessage
 import com.aallam.openai.api.chat.ChatRole
 import com.aallam.openai.api.chat.ToolCall
+import com.aallam.openai.api.chat.ToolChoice
 import com.aallam.openai.api.core.Usage
 import com.aallam.openai.api.model.ModelId
 import io.ktor.util.collections.ConcurrentSet
@@ -284,6 +285,7 @@ internal object ConversationEngine {
             temperature = endpoint.temperature,
             messages = history,
             tools = availableTools,
+            toolChoice = ToolChoice.Required,
         )
         JChatGPT.logger.info("API Requesting... Model=${endpoint.model} [${endpoint.label}]")
         return endpoint.service.chatCompletions(request, onCacheUsage)
diff --git a/src/test/kotlin/llm/ModelServiceTest.kt b/src/test/kotlin/llm/ModelServiceTest.kt
index cc8ebdd..f218a66 100644
--- a/src/test/kotlin/llm/ModelServiceTest.kt
+++ b/src/test/kotlin/llm/ModelServiceTest.kt
@@ -2,6 +2,7 @@ package top.jie65535.mirai.llm
 
 import com.aallam.openai.api.chat.ChatCompletionRequest
 import com.aallam.openai.api.chat.ChatMessage
+import com.aallam.openai.api.chat.ToolChoice
 import com.aallam.openai.api.model.ModelId
 import com.sun.net.httpserver.HttpServer
 import io.ktor.utils.io.ByteReadChannel
@@ -96,6 +97,23 @@ class ModelServiceTest {
         )
     }
 
+    @Test
+    fun serializesRequiredToolChoice() {
+        val body = service.buildRequestBody(
+            request = ChatCompletionRequest(
+                model = ModelId("test-model"),
+                messages = listOf(ChatMessage.User("hello")),
+                toolChoice = ToolChoice.Required,
+            ),
+            stream = true,
+        )
+
+        assertEquals(
+            "required",
+            Json.parseToJsonElement(body).jsonObject.getValue("tool_choice").jsonPrimitive.content,
+        )
+    }
+
     @Test
     fun acceptsStandaloneUsageAndEmptyHeartbeatEvents() {
         assertNull(service.decodeStreamChunk("{}"))