diff --git a/components/heap/multi_heap_poisoning.c b/components/heap/multi_heap_poisoning.c
index ec620c079..9a9d739ad 100644
--- a/components/heap/multi_heap_poisoning.c
+++ b/components/heap/multi_heap_poisoning.c
@@ -355,9 +355,11 @@ void *multi_heap_get_block_owner(multi_heap_block_handle_t block)
 
 multi_heap_handle_t multi_heap_register(void *start, size_t size)
 {
+#ifdef SLOW
     if (start != NULL) {
         memset(start, FREE_FILL_PATTERN, size);
     }
+#endif
     return multi_heap_register_impl(start, size);
 }