diff --git a/app/src/processing/app/Base.java b/app/src/processing/app/Base.java
index aa9de756f..d6bbb89d9 100644
--- a/app/src/processing/app/Base.java
+++ b/app/src/processing/app/Base.java
@@ -357,6 +357,9 @@ public class Base {
           currentDirectory = args[i];
         continue;
       }
+      if (args[i].startsWith("--"))
+        showError(null, I18n.format(_("unknown option: {0}"), args[i]), null);
+
       String path = args[i];
       // Fix a problem with systems that use a non-ASCII languages. Paths are
       // being passed in with 8.3 syntax, which makes the sketch loader code