diff --git a/main.go b/main.go
index 2f6be25..525085c 100644
--- a/main.go
+++ b/main.go
@@ -25,6 +25,10 @@ func loadEnv() {
 		log.Fatal("You're missing one (or more) required env vars: 'SQLITE_PATH, DOMAIN, PORT, CSRF_KEY'.")
 	}
 
+	if PORT, err := strconv.ParseInt(os.Getenv("PORT"), 10, 64); PORT <= 0 || err != nil {
+		log.Fatal("Invalid PORT env var.")
+	}
+
 	port, err := strconv.ParseUint(os.Getenv("PORT"), 10, 32)
 	if err != nil {
 		log.Fatal("Invalid PORT value. Make sure it's a valid port.")