tool/mk_builtin_loader.rb: check if op is an array or not

The insn array includes not only an array but also some literal objects.

1 files changed, 1 insertions, 1 deletions

diff --git a/tool/mk_builtin_loader.rb b/tool/mk_builtin_loader.rb
index cea4d1f99b..87b5e2ab76 100644
--- a/tool/mk_builtin_loader.rb
+++ b/tool/mk_builtin_loader.rb
@@ -18,7 +18,7 @@ def collect_builtin iseq_ary, bs
       end
     else
       insn[1..-1].each{|op|
-        if op[0] == "YARVInstructionSequence/SimpleDataFormat"
+        if op.is_a?(Array) && op[0] == "YARVInstructionSequence/SimpleDataFormat"
           collect_builtin op, bs
         end
       }