diff --git a/libraries/SITL/SITL.h b/libraries/SITL/SITL.h
index b3eb69aa1c..5ca4b84556 100644
--- a/libraries/SITL/SITL.h
+++ b/libraries/SITL/SITL.h
@@ -125,7 +125,7 @@ public:
     AP_Int16 flow_rate; // optflow data rate (Hz)
     AP_Int8  flow_delay; // optflow data delay
     AP_Int8  terrain_enable; // enable using terrain for height
-    AP_Int8  pin_mask; // for GPIO emulation
+    AP_Int16 pin_mask; // for GPIO emulation
     AP_Float speedup; // simulation speedup
     AP_Int8  odom_enable; // enable visual odomotry data