diff --git a/backend/hp3900_rts8822.c b/backend/hp3900_rts8822.c
index c3b458c5a..0d16fd85e 100644
--- a/backend/hp3900_rts8822.c
+++ b/backend/hp3900_rts8822.c
@@ -11576,6 +11576,7 @@ Calib_LoadConfig (struct st_device *dev,
   calibcfg->BShadingDefCutOff =
     get_value (section, BSHADINGDEFCUTOFF, 0, FITCALIBRATE);
 
+  refcfg.extern_boundary = 0;
   cfg_autoref_get (&refcfg);
   calibcfg->ExternBoundary = refcfg.extern_boundary * 0.01;