diff --git a/src/main/java/de/bixilon/minosoft/data/assets/AssetsManager.java b/src/main/java/de/bixilon/minosoft/data/assets/AssetsManager.java
index f2ab8639f..dc041f620 100644
--- a/src/main/java/de/bixilon/minosoft/data/assets/AssetsManager.java
+++ b/src/main/java/de/bixilon/minosoft/data/assets/AssetsManager.java
@@ -303,6 +303,7 @@ public class AssetsManager {
         if (verifyAssetHash(hash)) {
             return;
         }
+        checkURL(url);
         Log.verbose(String.format("Downloading %s -> %s", url, hash));
         if (compressed) {
             Util.downloadFileAsGz(url, getAssetDiskPath(hash));
@@ -317,4 +318,10 @@ public class AssetsManager {
         }
         return StaticConfiguration.HOME_DIRECTORY + String.format("assets/objects/%s/%s.gz", hash.substring(0, 2), hash);
     }
+
+    private static void checkURL(String url) {
+        if (!url.startsWith("http://") && !url.startsWith("https://")) {
+            throw new IllegalArgumentException("Not a valid url:" + url);
+        }
+    }
 }