diff --git a/src/sim_client.c b/src/sim_client.c
index ca76aed2..15312a06 100644
--- a/src/sim_client.c
+++ b/src/sim_client.c
@@ -6,8 +6,6 @@
 #define CHANNEL_LOOKUP_BUCKETS 4096
 
 /* Offset in bytes from start of store struct to start of clients array (assume adjacently allocated) */
-
-/* FIXME: Incorrect since buckets are also allocated */
 #define STORE_CLIENTS_OFFSET (sizeof(struct sim_client_store) + (sizeof(struct sim_client_store) % alignof(struct sim_client)))
 
 
@@ -22,11 +20,17 @@ READONLY struct sim_client_store _g_sim_client_store_nil = { .valid = false };
 struct sim_client_store *client_store_alloc(void)
 {
     struct arena arena = arena_alloc(GIGABYTE(64));
+    u64 num_channel_lookup_buckets = CHANNEL_LOOKUP_BUCKETS;
+    u64 channel_lookup_buckets = arena_push_array_zero(&arena, struct channel_lookup_bucket, num_channel_lookup_buckets);
+
     struct sim_client_store *store = arena_push_zero(&arena, struct sim_client_store);
-    store->arena = arena;
-    store->num_channel_lookup_buckets = CHANNEL_LOOKUP_BUCKETS;
-    store->channel_lookup_buckets = arena_push_array_zero(&arena, struct channel_lookup_bucket, store->num_channel_lookup_buckets);
     store->clients = arena_dry_push(&arena, struct sim_client);
+    ASSERT((u8 *)store->clients - (u8 *)store == STORE_CLIENTS_OFFSET);  /* Offset must be correct */
+
+    store->arena = arena;
+    store->num_channel_lookup_buckets = num_channel_lookup_buckets;
+    store->channel_lookup_buckets = channel_lookup_buckets;
+
     return store;
 }
 
diff --git a/src/sim_ent.c b/src/sim_ent.c
index 53678044..706d1a39 100644
--- a/src/sim_ent.c
+++ b/src/sim_ent.c
@@ -44,7 +44,7 @@ struct sim_ent_store *sim_ent_store_alloc(void)
     store->valid = true;
     store->arena = arena;
     store->entities = arena_dry_push(&arena, struct sim_ent);
-    ASSERT((u64)store->entities - (u64)store == STORE_ENTITIES_OFFSET);  /* Offset must be correct */
+    ASSERT((u8 *)store->entities - (u8 *)store == STORE_ENTITIES_OFFSET);  /* Offset must be correct */
     store_make_root(store);
     return store;
 }