diff --git a/libraries/AP_NavEKF3/AP_NavEKF3.cpp b/libraries/AP_NavEKF3/AP_NavEKF3.cpp
index 324d7a7af7..bbf69fb3a5 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3.cpp
+++ b/libraries/AP_NavEKF3/AP_NavEKF3.cpp
@@ -125,6 +125,11 @@
 #define EK3_PRIMARY_DEFAULT 0
 #endif
 
+// This allows boards to default to using a specified number of IMUs and EKF lanes
+#ifndef HAL_EKF_IMU_MASK_DEFAULT
+#define HAL_EKF_IMU_MASK_DEFAULT 3       // Default to using two IMUs
+#endif
+
 // Define tuning parameters
 const AP_Param::GroupInfo NavEKF3::var_info[] = {
 
@@ -402,7 +407,7 @@ const AP_Param::GroupInfo NavEKF3::var_info[] = {
     // @Bitmask: 0:FirstIMU,1:SecondIMU,2:ThirdIMU,3:FourthIMU,4:FifthIMU,5:SixthIMU
     // @User: Advanced
     // @RebootRequired: True
-    AP_GROUPINFO("IMU_MASK",     33, NavEKF3, _imuMask, 3),
+    AP_GROUPINFO("IMU_MASK",     33, NavEKF3, _imuMask, HAL_EKF_IMU_MASK_DEFAULT),
     
     // @Param: CHECK_SCALE
     // @DisplayName: GPS accuracy check scaler (%)