diff --git a/.gitignore b/.gitignore
index 577a4f199..c09c7071c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,4 +11,4 @@ node_modules/
 .eslintcache
 
 # build output
-dist/
\ No newline at end of file
+dist/.DS_Store
diff --git a/src/routes/messages/non-stream-translation.ts b/src/routes/messages/non-stream-translation.ts
index dc41e6382..b441e763b 100644
--- a/src/routes/messages/non-stream-translation.ts
+++ b/src/routes/messages/non-stream-translation.ts
@@ -239,11 +239,26 @@ function translateAnthropicToolsToOpenAI(
     function: {
       name: tool.name,
       description: tool.description,
-      parameters: tool.input_schema,
+      parameters: normalizeToolParameters(tool.input_schema),
     },
   }))
 }
 
+function normalizeToolParameters(
+  inputSchema: unknown,
+): Record<string, unknown> {
+  if (!inputSchema || typeof inputSchema !== "object") {
+    return { type: "object", properties: {} }
+  }
+
+  const schema = { ...inputSchema } as Record<string, unknown>
+  if (schema.type === "object" && schema.properties === undefined) {
+    return { ...schema, properties: {} }
+  }
+
+  return schema
+}
+
 function translateAnthropicToolChoiceToOpenAI(
   anthropicToolChoice: AnthropicMessagesPayload["tool_choice"],
 ): ChatCompletionsPayload["tool_choice"] {