diff --git a/libraries/AP_NavEKF2/AP_NavEKF2.cpp b/libraries/AP_NavEKF2/AP_NavEKF2.cpp
index 8455943b16..0719505b90 100644
--- a/libraries/AP_NavEKF2/AP_NavEKF2.cpp
+++ b/libraries/AP_NavEKF2/AP_NavEKF2.cpp
@@ -117,6 +117,11 @@
 
 #endif // APM_BUILD_DIRECTORY
 
+// 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
+
 extern const AP_HAL::HAL& hal;
 
 // Define tuning parameters
@@ -408,7 +413,7 @@ const AP_Param::GroupInfo NavEKF2::var_info[] = {
     // @Bitmask: 0:FirstIMU,1:SecondIMU,2:ThirdIMU,3:FourthIMU,4:FifthIMU,5:SixthIMU
     // @User: Advanced
     // @RebootRequired: True
-    AP_GROUPINFO("IMU_MASK",     33, NavEKF2, _imuMask, 3),
+    AP_GROUPINFO("IMU_MASK",     33, NavEKF2, _imuMask, HAL_EKF_IMU_MASK_DEFAULT),
     
     // @Param: CHECK_SCALE
     // @DisplayName: GPS accuracy check scaler (%)