diff --git a/src/lib/malloc/map_anon.c b/src/lib/malloc/map_anon.c
index f4fda00bff..6afea713df 100644
--- a/src/lib/malloc/map_anon.c
+++ b/src/lib/malloc/map_anon.c
@@ -70,6 +70,11 @@
#endif
+#if defined(HAVE_MINHERIT) && !defined(FLAG_ZERO) && !defined(FLAG_NOINHERIT)
+#warn "minherit() is defined, but we couldn't find the right flag for it."
+#warn "This is probably a bug in Tor's support for this platform."
+#endif
+
/**
* Helper: try to prevent the sz bytes at mem from being swapped
* to disk. Return 0 on success or if the facility is not available on this