diff --git a/src/small_allocator.c b/src/small_allocator.c
index e67ab11..5e64353 100644
--- a/src/small_allocator.c
+++ b/src/small_allocator.c
@@ -73,14 +73,15 @@ void small_allocator_init(SmallAllocator* a, void* backing_store, size_t size)
 {
     // backing store must be aligned, otherwise  all alignment guarantees are lies
     assert(((uintptr_t)backing_store & (ALIGNMENT - 1)) == 0);
+    assert(size >= sizeof(BlockHeader));
 
-    a->base = (uint8_t*)backing_store;
+    a->base = backing_store;
     a->size = size;
 
-    BlockHeader* first = (BlockHeader*)a->base;
+    BlockHeader* first = backing_store;
     size_t usable = ALIGN(size - sizeof(BlockHeader));
-
-    first->size_and_flags = usable | BLOCK_FREE;
+    block_set_free(first);
+    block_set_size(first, usable);
     first->next = NULL;
     first->prev = NULL;