diff --git a/main.go b/main.go
index 688b3f8..cca2f54 100644
--- a/main.go
+++ b/main.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"log"
 	"net/http"
+	"net/url"
 	"os"
 	"strings"
 
@@ -42,7 +43,7 @@ func WebhookHandler(w http.ResponseWriter, r *http.Request) {
 
 		req, err := http.NewRequest("POST", os.Getenv("NTFY_TOPIC"), strings.NewReader(alert.Annotations["description"]))
 		if err != nil {
-			log.Printf("Building request to %s failed: %s", req.RemoteAddr, err)
+			log.Printf("Building request failed: %s", err)
 			w.WriteHeader(http.StatusBadRequest)
 			return
 		}
@@ -90,6 +91,11 @@ func main() {
 		}
 	}
 
+	_, err := url.Parse(os.Getenv("NTFY_TOPIC"))
+	if err != nil {
+		log.Fatal("Environment variable NTFY_TOPIC is not a valid URL")
+	}
+
 	http.HandleFunc("/", WebhookHandler)
 	var listenAddr = fmt.Sprintf("%v:%v", os.Getenv("HTTP_ADDRESS"), os.Getenv("HTTP_PORT"))
 	log.Printf("Listening for HTTP requests (webhooks) on %v\n", listenAddr)