Index: sys/kern/subr_gtaskqueue.c
===================================================================
--- sys/kern/subr_gtaskqueue.c
+++ sys/kern/subr_gtaskqueue.c
@@ -797,6 +797,8 @@
 					qid = i;
 					break;
 				}
+			if (i == qgroup->tqg_cnt)
+				panic("taskqgroup_adjust: Failed to pick a qid.");
 		}
 		qgroup->tqg_queue[qid].tgc_cnt++;
 		LIST_INSERT_HEAD(&qgroup->tqg_queue[qid].tgc_tasks, gtask,
Index: sys/net/iflib.c
===================================================================
--- sys/net/iflib.c
+++ sys/net/iflib.c
@@ -4303,7 +4303,8 @@
 	/* clear up to the qid'th bit */
 	for (i = 0; i < qid; i++) {
 		cpuid = CPU_FFS(cpus);
-		CPU_CLR(cpuid, cpus);
+		KASSERT(cpuid != 0, ("find_nth: No CPU %d", i));
+		CPU_CLR(cpuid - 1, cpus);
 	}
 }
 
@@ -4317,7 +4318,7 @@
 	iflib_filter_info_t info;
 	cpuset_t cpus;
 	gtask_fn_t *fn;
-	int tqrid, err;
+	int tqrid, err, cpu;
 	void *q;
 
 	info = &ctx->ifc_filter_info;
@@ -4364,7 +4365,9 @@
 		return (err);
 	if (tqrid != -1) {
 		find_nth(ctx, &cpus, qid);
-		taskqgroup_attach_cpu(tqg, gtask, q, CPU_FFS(&cpus), irq->ii_rid, name);
+		cpu = CPU_FFS(&cpus);
+		KASSERT(cpu != 0, ("no CPU at qid %d", qid));
+		taskqgroup_attach_cpu(tqg, gtask, q, cpu - 1, irq->ii_rid, name);
 	} else
 		taskqgroup_attach(tqg, gtask, q, tqrid, name);