diff --git a/src/agents/ollama-stream.ts b/src/agents/ollama-stream.ts
index f332ad1fd83..c06d0193279 100644
--- a/src/agents/ollama-stream.ts
+++ b/src/agents/ollama-stream.ts
@@ -216,6 +216,19 @@ interface OllamaChatResponse {
   eval_duration?: number;
 }
 
+// ── Helpers ──────────────────────────────────────────────────────────────────
+
+function parseToolArgs(raw: unknown): Record<string, unknown> {
+  if (typeof raw === "string") {
+    try {
+      return JSON.parse(raw) as Record<string, unknown>;
+    } catch {
+      return {};
+    }
+  }
+  return (raw as Record<string, unknown>) ?? {};
+}
+
 // ── Message conversion ──────────────────────────────────────────────────────
 
 type InputContentPart =
@@ -254,9 +267,9 @@ function extractToolCalls(content: unknown): OllamaToolCall[] {
   const result: OllamaToolCall[] = [];
   for (const part of parts) {
     if (part.type === "toolCall") {
-      result.push({ function: { name: part.name, arguments: part.arguments } });
+      result.push({ function: { name: part.name, arguments: parseToolArgs(part.arguments) } });
     } else if (part.type === "tool_use") {
-      result.push({ function: { name: part.name, arguments: part.input } });
+      result.push({ function: { name: part.name, arguments: part.input ?? {} } });
     }
   }
   return result;
@@ -355,7 +368,7 @@ export function buildAssistantMessage(
         type: "toolCall",
         id: `ollama_call_${randomUUID()}`,
         name: tc.function.name,
-        arguments: tc.function.arguments,
+        arguments: parseToolArgs(tc.function.arguments),
       });
     }
   }