diff --git a/src/qwen-delegate.ts b/src/qwen-delegate.ts
index 04317a9..b76d63d 100644
--- a/src/qwen-delegate.ts
+++ b/src/qwen-delegate.ts
@@ -25,15 +25,22 @@ const DEFAULT_TIMEOUT_MS = 10 * 60 * 1000; // 10 min
  * qwen-code prints startup warnings (e.g. failed MCP sub-servers) to stderr; those are
  * ignored on success and surfaced only when the run itself fails.
  */
-export function delegateToQwen (
+export function delegateToQwen(
   prompt: string,
   options: DelegateOptions = {},
 ): Promise<DelegateResult> {
   const { timeoutMs = DEFAULT_TIMEOUT_MS, spawnFn = spawn } = options;
 
   return new Promise((resolve) => {
-    const child: ChildProcess = spawnFn("qwen", ["-p", prompt], {
-      shell: true, // qwen.cmd on Windows needs a shell to resolve
+    // shell:true is required for qwen.cmd to resolve on Windows, but Node does NOT escape
+    // array args in that mode (see DEP0190) — it just space-joins them, so an unquoted
+    // multi-word prompt silently splits into extra positional args and confuses qwen's CLI
+    // parser ("Cannot use both a positional prompt and the --prompt (-p) flag together").
+    // Build the command as a single, explicitly-quoted string instead.
+    const quoteArg = (s: string) => `"${s.replace(/"/g, '\\"')}"`;
+    const command = ["qwen", "-p", quoteArg(prompt)].join(" ");
+    const child: ChildProcess = spawnFn(command, {
+      shell: true,
       stdio: ["ignore", "pipe", "pipe"],
     });