Index: hostapd-2021-02-20-59e9794c/src/ap/hostapd.c
===================================================================
--- hostapd-2021-02-20-59e9794c.orig/src/ap/hostapd.c
+++ hostapd-2021-02-20-59e9794c/src/ap/hostapd.c
@@ -3814,6 +3814,8 @@ hostapd_switch_channel_fallback(struct h
 				const struct hostapd_freq_params *freq_params)
 {
 	int seg0_idx = 0, seg1_idx = 0, bw = CHANWIDTH_USE_HT;
+	u8 op_class;
+	u8 chan;
 
 	wpa_printf(MSG_DEBUG, "Restarting all CSA-related BSSes");
 
@@ -3846,6 +3848,11 @@ hostapd_switch_channel_fallback(struct h
 	iface->freq = freq_params->freq;
 	iface->conf->channel = freq_params->channel;
 	iface->conf->secondary_channel = freq_params->sec_channel_offset;
+	ieee80211_freq_to_channel_ext(freq_params->freq, freq_params->sec_channel_offset, bw, &op_class, &chan);
+	if (chan != freq_params->channel)
+		wpa_printf(MSG_ERROR, "Channel mismatch: %d -> %d", freq_params->channel, chan);
+
+	iface->conf->op_class = op_class;
 	hostapd_set_oper_centr_freq_seg0_idx(iface->conf, seg0_idx);
 	hostapd_set_oper_centr_freq_seg1_idx(iface->conf, seg1_idx);
 	hostapd_set_oper_chwidth(iface->conf, bw);