diff --git a/tests/try-syscall.c b/tests/try-syscall.c
index 84a0ca66..df350542 100644
--- a/tests/try-syscall.c
+++ b/tests/try-syscall.c
@@ -7,6 +7,9 @@
  *
  * In general, we pass a bad fd or pointer to each syscall that will
  * accept one, so that it will fail with EBADF or EFAULT without side-effects.
+ *
+ * This helper is used for regression tests in both bubblewrap and flatpak.
+ * Please keep both copies in sync.
  */
 
 #include <errno.h>