diff --git a/src/tools/opensc-explorer.c b/src/tools/opensc-explorer.c

index d251495c..e48f3189 100644

--- a/src/tools/opensc-explorer.c

+++ b/src/tools/opensc-explorer.c

@@ -2030,9 +2030,9 @@ static int do_put_data(int argc, char **argv)

 static int do_apdu(int argc, char **argv)

 {

 	sc_apdu_t apdu;

-	u8 buf[SC_MAX_EXT_APDU_BUFFER_SIZE];

+	u8 buf[SC_MAX_EXT_APDU_BUFFER_SIZE] = {0};

 	u8 rbuf[SC_MAX_EXT_APDU_BUFFER_SIZE];

-	size_t len, i;

+	size_t len = 0, i;

 	int r;

 	if (argc < 1)