diff --git a/src/stk500.c b/src/stk500.c
index 461d1627..d45a6ef7 100644
--- a/src/stk500.c
+++ b/src/stk500.c
@@ -680,7 +680,7 @@ static int stk500_parseextparms(const PROGRAMMER *pgm, const LISTID extparms)
 
     else if (str_starts(extended_param, "varef")) {
       if (pgm->extra_features & HAS_VAREF_ADJ) {
-        int sscanf_success;
+        int sscanf_success = 0;
         double varef_set_val = 0;
         // Get new analog reference voltage for channel 0
         if (str_starts(extended_param, "varef=")) {
diff --git a/src/stk500v2.c b/src/stk500v2.c
index 6f39b446..acd76744 100644
--- a/src/stk500v2.c
+++ b/src/stk500v2.c
@@ -1844,7 +1844,7 @@ static int stk500v2_parseextparms(const PROGRAMMER *pgm, const LISTID extparms)
 
     else if (str_starts(extended_param, "varef")) {
       if (pgm->extra_features & HAS_VAREF_ADJ) {
-        int sscanf_success;
+        int sscanf_success = 0;
         double varef_set_val = 0;
         // Get new analog reference voltage for channel 0
         if (str_starts(extended_param, "varef=")) {