diff --git a/libraries/AP_GPS/AP_GPS.cpp b/libraries/AP_GPS/AP_GPS.cpp
index e8ce61412b..1d655e7c30 100644
--- a/libraries/AP_GPS/AP_GPS.cpp
+++ b/libraries/AP_GPS/AP_GPS.cpp
@@ -291,6 +291,8 @@ AP_GPS::update(void)
             primary_instance = i;
         }
     }
+#else
+    num_instances = 1;
 #endif // GPS_MAX_INSTANCES
 }