diff --git a/httpd/page_impl.c b/httpd/page_impl.c
index c0d9e0b..42c3503 100644
--- a/httpd/page_impl.c
+++ b/httpd/page_impl.c
@@ -643,7 +643,7 @@ void send_stp(void)
 		itoa_html(stp_pp2p[pi_i]);
 		/* designated info: a freshly heard BPDU wins, else we are the
 		 * segment's designated bridge and report our own values */
-		stp_we_root = stp_dbridge[pi_i].mac[5] && stp_bpdu_age[pi_i] < (uint16_t)stp_maxage_s * 64;
+		stp_we_root = stp_dbridge[pi_i].mac[5] && stp_bpdu_age[pi_i] < (uint16_t)stp_maxage_s * STP_HZ;
 		slen += strtox(outbuf + slen, ",\"db\":\"");
 		if (stp_we_root) {
 			pi_prio = stp_dbridge[pi_i].prio; pi_ext = stp_dbridge[pi_i].ext;
diff --git a/rtl837x_stp.c b/rtl837x_stp.c
index 610dcc7..be3f79b 100644
--- a/rtl837x_stp.c
+++ b/rtl837x_stp.c
@@ -101,8 +101,6 @@ __xdata uint16_t stp_tc_while;		/* ticks left to set the TC flag in our BPDUs */
 __xdata uint8_t  stp_i;		/* shared loop iterator (DSEG relief) */
 __xdata uint32_t stp_cost_scratch;
 
-/* stp_timers() runs at ~64 Hz (main loop ~256 Hz / (STP_TICK_DIVIDER+1)) */
-#define STP_HZ		64
 #define STP_EDGE_DELAY	(3 * STP_HZ)	/* auto-edge: forward after 3 s without BPDU */
 
 #define AUTO_COST	20000UL		/* path cost used when stp_pcost == 0 (1G default) */
diff --git a/rtl837x_stp.h b/rtl837x_stp.h
index 56aea9d..ce09b69 100644
--- a/rtl837x_stp.h
+++ b/rtl837x_stp.h
@@ -9,6 +9,13 @@ void stp_off(void) __banked;
 void stp_parse(void) __banked __reentrant;	/* "stp ..." CLI handler (cmd_parser delegates here) */
 void stp_defaults(void) __banked;	/* boot init: 802.1D/w default configuration */
 
+/* Tick rate of stp_timers(): the main loop idles on the 200 Hz system tick
+ * and rtlplayground.c calls us every (STP_TICK_DIVIDER + 1) = 4th pass.
+ * Measured on hardware: hello 2 s produced BPDUs exactly 2.560 s apart with
+ * the previous value of 64, i.e. 20 ms per tick - every configured timer ran
+ * 28 % long. Shared with the web UI, which ages the same counters. */
+#define STP_HZ 50
+
 /* Bridge identifier as carried in a BPDU (priority, extension, MAC). */
 struct bridge {
 	uint8_t prio;