diff --git a/README.md b/README.md
index 5815631..d0041e2 100644
--- a/README.md
+++ b/README.md
@@ -185,6 +185,8 @@ extended tests supported by both protocols. Each target sets its endpoint,
 protocol, and test config explicitly, regardless of the container defaults.
 The browser target runs in a pinned Playwright container, installs its node
 packages there, and uses the account generated when `nictool-legacy` starts.
+The legacy profile opts into that account with `NICTOOL_TEST_ENV=1`; NicTool's
+standalone container leaves it disabled unless requested.
 
 ## Local development
 
diff --git a/docker-compose.yml b/docker-compose.yml
index f2fe2c6..919cc57 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -149,6 +149,7 @@ services:
       NICTOOL_DATA_PROTOCOL: ${NICTOOL_DATA_PROTOCOL:-rest}
       NICTOOL_SERVER_HOST: ${NICTOOL_SERVER_HOST:-api}
       NICTOOL_SERVER_PORT: ${NICTOOL_SERVER_PORT:-3000}
+      NICTOOL_TEST_ENV: "1"
     healthcheck:
       test: ["CMD", "curl", "-fso", "/dev/null", "http://localhost/index.cgi"]
       interval: 10s
diff --git a/tests/test_compose.py b/tests/test_compose.py
index 7fe3c92..0a888c2 100644
--- a/tests/test_compose.py
+++ b/tests/test_compose.py
@@ -65,6 +65,11 @@ def test_legacy_waits_for_the_root_user_seed(self):
             "service_completed_successfully",
         )
 
+    def test_legacy_profile_enables_the_generated_test_environment(self):
+        legacy = compose()["services"]["nictool-legacy"]
+
+        self.assertEqual(legacy["environment"]["NICTOOL_TEST_ENV"], "1")
+
     def test_browser_runner_stays_out_of_the_all_profile(self):
         self.assertEqual(compose()["services"]["v2-e2e"]["profiles"], ["test"])