diff --git a/libraries/AP_IOMCU/AP_IOMCU.cpp b/libraries/AP_IOMCU/AP_IOMCU.cpp
index 73f283532f2b99..0d545bd78a7776 100644
--- a/libraries/AP_IOMCU/AP_IOMCU.cpp
+++ b/libraries/AP_IOMCU/AP_IOMCU.cpp
@@ -791,7 +791,7 @@ bool AP_IOMCU::modify_register(uint8_t page, uint8_t offset, uint16_t clearbits,
 
 void AP_IOMCU::write_channel(uint8_t chan, uint16_t pwm)
 {
-    if (chan >= IOMCU_MAX_CHANNELS) {
+    if (chan >= IOMCU_MAX_RC_CHANNELS) {    // could be SBUS out
         return;
     }
     if (chan >= pwm_out.num_channels) {
@@ -1112,7 +1112,7 @@ bool AP_IOMCU::check_crc(void)
 void AP_IOMCU::set_failsafe_pwm(uint16_t chmask, uint16_t period_us)
 {
     bool changed = false;
-    for (uint8_t i=0; i<IOMCU_MAX_CHANNELS; i++) {
+    for (uint8_t i=0; i<IOMCU_MAX_RC_CHANNELS; i++) {
         if (chmask & (1U<<i)) {
             if (pwm_out.failsafe_pwm[i] != period_us) {
                 pwm_out.failsafe_pwm[i] = period_us;
diff --git a/libraries/AP_IOMCU/AP_IOMCU.h b/libraries/AP_IOMCU/AP_IOMCU.h
index 253b1b9890b457..5199c5fb3dbdb8 100644
--- a/libraries/AP_IOMCU/AP_IOMCU.h
+++ b/libraries/AP_IOMCU/AP_IOMCU.h
@@ -243,9 +243,9 @@ class AP_IOMCU
     // output pwm values
     struct {
         uint8_t num_channels;
-        uint16_t pwm[IOMCU_MAX_CHANNELS];
+        uint16_t pwm[IOMCU_MAX_RC_CHANNELS];
         uint16_t safety_mask;
-        uint16_t failsafe_pwm[IOMCU_MAX_CHANNELS];
+        uint16_t failsafe_pwm[IOMCU_MAX_RC_CHANNELS];
         uint8_t failsafe_pwm_set;
         uint8_t failsafe_pwm_sent;
         uint16_t channel_mask;
@@ -253,7 +253,7 @@ class AP_IOMCU
 
     // read back pwm values
     struct {
-        uint16_t pwm[IOMCU_MAX_CHANNELS];
+        uint16_t pwm[IOMCU_MAX_RC_CHANNELS];
     } pwm_in;
 
     // output rates