diff --git a/compiler/tests-jsoo/flush_stubs.c b/compiler/tests-jsoo/flush_stubs.c
index 006fcf8191..099b0927d6 100644
--- a/compiler/tests-jsoo/flush_stubs.c
+++ b/compiler/tests-jsoo/flush_stubs.c
@@ -4,6 +4,7 @@
 #include "caml/memory.h"
 
 CAMLprim value flush_stdout_stderr (value unit) {
+  (void)unit;
   CAMLparam0 ();   /* v is ignored */
   fflush(stderr);
   fflush(stdout);