diff --git a/bench/bench-mlib.c b/bench/bench-mlib.c
index 8c3b9a0c..01f0bf59 100644
--- a/bench/bench-mlib.c
+++ b/bench/bench-mlib.c
@@ -116,7 +116,8 @@ test_dict(unsigned long  n)
 #endif
   M_LET(dict, DICT_OPLIST(ulong)) {
     for (size_t i = 0; i < n; i++) {
-      dict_ulong_set_at(dict, rand_get(), rand_get() );
+      unsigned long key = rand_get();
+      dict_ulong_set_at(dict, key, rand_get() );
     }
     rand_init();
     unsigned int s = 0;