diff --git a/ufw-docker b/ufw-docker
index 2d3bee2..e9ecae7 100755
--- a/ufw-docker
+++ b/ufw-docker
@@ -44,7 +44,9 @@ function ufw-docker--allow() {
     docker inspect "$INSTANCE_NAME" &>/dev/null ||
         die "Docker instance \"$INSTANCE_NAME\" doesn't exist."
 
-    mapfile -t INSTANCE_IP_ADDRESSES < <(docker inspect --format='{{range .NetworkSettings.Networks}}{{.IPAddress}}{{"\n"}}{{end}}' "$INSTANCE_NAME" | remove_blank_lines)
+    mapfile -t INSTANCE_IP_ADDRESSES < <(docker inspect --format='{{range .NetworkSettings.Networks}}{{.IPAddress}}{{"\n"}}{{end}}' "$INSTANCE_NAME" 2>/dev/null | remove_blank_lines)
+
+    [[ -z "${INSTANCE_IP_ADDRESSES:-}" ]] && die "Could not find a running instance \"$INSTANCE_NAME\"."
 
     mapfile -t PORT_PROTO_LIST < <(docker inspect --format='{{range $p, $conf := .NetworkSettings.Ports}}{{with $conf}}{{$p}}{{"\n"}}{{end}}{{end}}' "$INSTANCE_NAME" | remove_blank_lines)