diff --git a/test/ruby/test_pack.rb b/test/ruby/test_pack.rb
index 86b34b3ba6..59edc3eb4b 100644
--- a/test/ruby/test_pack.rb
+++ b/test/ruby/test_pack.rb
@@ -714,4 +714,9 @@ EXPECTED
     $VERBOSE = verbose
   end
 
+  def test_invalid_warning
+    assert_warning(/unknown pack directive ',' in ','/) {
+      [].pack(",")
+    }
+  end
 end