diff --git a/frankenphp_test.go b/frankenphp_test.go
index 4d5e97779..731fa32e8 100644
--- a/frankenphp_test.go
+++ b/frankenphp_test.go
@@ -672,11 +672,12 @@ func TestFailingWorker(t *testing.T) {
 }
 
 func TestEnv(t *testing.T) {
-	testEnv(t, &testOptions{})
+	testEnv(t, &testOptions{nbParallelRequests:1})
 }
 func TestEnvWorker(t *testing.T) {
-	testEnv(t, &testOptions{workerScript: "env/test-env.php"})
+	testEnv(t, &testOptions{nbParallelRequests:1, workerScript: "env/test-env.php"})
 }
+// testEnv cannot be run in parallel due to https://github.com/golang/go/issues/63567
 func testEnv(t *testing.T, opts *testOptions) {
 	assert.NoError(t, os.Setenv("EMPTY", ""))