diff --git a/src/main/java/com/cloudbees/jenkins/plugins/docker_build_env/Docker.java b/src/main/java/com/cloudbees/jenkins/plugins/docker_build_env/Docker.java
index e19c0eb..ba508b5 100644
--- a/src/main/java/com/cloudbees/jenkins/plugins/docker_build_env/Docker.java
+++ b/src/main/java/com/cloudbees/jenkins/plugins/docker_build_env/Docker.java
@@ -294,6 +294,11 @@ private String getDocker0Ip(Launcher launcher, String image) throws IOException,
 
         String route = out.toString("UTF-8").trim();
 
+        // ensures that the the default IP exists so that the return is not null
+        if (!route.contains("default")) {
+            throw new RuntimeException("Default IP does not exist");
+        }
+
         // equivalent to `awk '/default/ { print $3 }'` but we can't assume awk is available
         String dockerhost = route.substring(route.indexOf("default")) .split(" ")[2];
         return dockerhost;