diff --git a/drivers/modem/alt1250/alt1250.c b/drivers/modem/alt1250/alt1250.c
index 97a4e7e2a7..336f941fd7 100644
--- a/drivers/modem/alt1250/alt1250.c
+++ b/drivers/modem/alt1250/alt1250.c
@@ -819,7 +819,7 @@ static int parse_altcompkt(FAR struct alt1250_dev_s *dev, FAR uint8_t *pkt,
   uint16_t cid = parse_cid(h);
   uint16_t tid = parse_tid(h);
   parse_handler_t parser;
-  FAR alt_evtbuf_inst_t *inst;
+  FAR alt_evtbuf_inst_t *inst = NULL;
   FAR void **outparam;
   size_t outparamlen;
 
@@ -912,7 +912,7 @@ static int parse_altcompkt(FAR struct alt1250_dev_s *dev, FAR uint8_t *pkt,
           *bitmap = ALT1250_EVTBIT_REPLY;
         }
     }
-  else
+  else if (inst != NULL)
     {
       /* Unlock outparam because it has been updated. */