diff --git a/bin/cli-main.ts b/bin/cli-main.ts
index fb04514..2e3bf68 100644
--- a/bin/cli-main.ts
+++ b/bin/cli-main.ts
@@ -2255,9 +2255,11 @@ export async function runCli() {
     } catch (error) {
       // Name where the bad value came from: an MCP host debugging a server
       // that will not start needs to know it is the environment, not a flag.
-      const source =
-        flagValue(process.argv, "--profile") === undefined ? "BETTERWRIGHT_PROFILE" : "--profile";
-      console.error(`${source}: ${error?.message || error}`);
+      // Launch-default errors already name their variable.
+      const message = String(error?.message || error);
+      const source = /^BETTERWRIGHT_[A-Z_]+ /.test(message) ? ""
+        : `${flagValue(process.argv, "--profile") === undefined ? "BETTERWRIGHT_PROFILE" : "--profile"}: `;
+      console.error(`${source}${message}`);
       return 1;
     }
   }
diff --git a/tests/node/cli-startup.test.ts b/tests/node/cli-startup.test.ts
index d128a10..bf18984 100644
--- a/tests/node/cli-startup.test.ts
+++ b/tests/node/cli-startup.test.ts
@@ -79,3 +79,29 @@ test("an absent or empty environment model still loads default model discovery",
     assert.match(result.stderr, /Unexpected setup module: .*doctor\.js/);
   }
 });
+
+test("invalid launch environment errors name their own variable, not the profile source", () => {
+  for (const [name, value, profileArgs] of [
+    ["BETTERWRIGHT_HEADLESS", "maybe", []],
+    ["BETTERWRIGHT_HEADLESS", "maybe", ["--profile", "work"]],
+    ["BETTERWRIGHT_DOWNLOAD_POLICY", "sometimes", []],
+  ] as const) {
+    const result = spawnSync(process.execPath, [cli, "run", ...profileArgs, "-c", "return 1"], {
+      cwd: root,
+      env: { ...process.env, BETTERWRIGHT_HOME: makeTempDir("betterwright-startup-home-"), BETTERWRIGHT_NO_DAEMON: "1", [name]: value },
+      encoding: "utf8",
+      timeout: 15_000,
+    });
+    assert.equal(result.status, 1);
+    assert.match(result.stderr, new RegExp(`^${name} must be`, "m"));
+    assert.doesNotMatch(result.stderr, /BETTERWRIGHT_PROFILE:|--profile:/);
+  }
+  const profile = spawnSync(process.execPath, [cli, "run", "-c", "return 1"], {
+    cwd: root,
+    env: { ...process.env, BETTERWRIGHT_HOME: makeTempDir("betterwright-startup-home-"), BETTERWRIGHT_NO_DAEMON: "1", BETTERWRIGHT_PROFILE: "../escape" },
+    encoding: "utf8",
+    timeout: 15_000,
+  });
+  assert.equal(profile.status, 1);
+  assert.match(profile.stderr, /^BETTERWRIGHT_PROFILE: /m);
+});