diff --git a/benchmarks/arms/baseline.js b/benchmarks/arms/baseline.js
index 1469035..7edada0 100644
--- a/benchmarks/arms/baseline.js
+++ b/benchmarks/arms/baseline.js
@@ -1,2 +1,6 @@
-// Baseline arm: no skill, just the task.
-module.exports = ({ vars }) => [{ role: 'user', content: vars.task }];
+// Baseline arm: no skill, with a one-line system prompt so the model doesn't ramble.
+const system = 'Provide just one example for any given task, and no commentary or usage examples.';
+module.exports = ({ vars }) => [
+  { role: 'system', content: system },
+  { role: 'user', content: vars.task },
+];