diff --git a/tools/sched_ext/scx_flatcg.bpf.c b/tools/sched_ext/scx_flatcg.bpf.c
index 0fd214cc61da..2d178c2ecacc 100644
--- a/tools/sched_ext/scx_flatcg.bpf.c
+++ b/tools/sched_ext/scx_flatcg.bpf.c
@@ -605,6 +605,9 @@ void BPF_STRUCT_OPS(fcg_cgroup_set_weight, struct cgroup *cgrp, u32 weight)
 		pcgc->child_weight_sum += (s64)weight - cgc->weight;
 	cgc->weight = weight;
 	bpf_spin_unlock(&cgv_tree_lock);
+
+	/* expire cached hweights so the new weight propagates */
+	__sync_fetch_and_add(&hweight_gen, 1);
 }
 
 static bool try_pick_next_cgroup(u64 *cgidp)