diff --git a/rigs/tentec/tt550.c b/rigs/tentec/tt550.c
index eade26be1..517d7fe78 100644
--- a/rigs/tentec/tt550.c
+++ b/rigs/tentec/tt550.c
@@ -812,7 +812,7 @@ tt550_set_tx_mode(RIG *rig, vfo_t vfo, rmode_t mode, pbwidth_t width)
     char ttmode;
     rmode_t saved_mode;
     pbwidth_t saved_width;
-    int mdbuf_len, ttfilter, retval;
+    int mdbuf_len, ttfilter=-1, retval;
     char mdbuf[48];
 
     switch (mode)