check.patch

diff --git a/core/src/main/java/org/jruby/RubyArray.java b/core/src/main/java/org/jruby/RubyArray.java
index 4148045..20765e48 100644
--- a/core/src/main/java/org/jruby/RubyArray.java
+++ b/core/src/main/java/org/jruby/RubyArray.java
@@ -2797,7 +2797,10 @@ public class RubyArray extends RubyObject implements List, RandomAccess {
                 IRubyObject tmp;
                 while (i < ary.realLength) {
                     IRubyObject elt = ary.values[ary.begin + i++];
-                    tmp = TypeConverter.checkArrayType(elt);
+
+                    tmp = context.nil;
+                    if(elt.respondsTo("to_ary"))
+                        tmp = TypeConverter.checkArrayType(elt);
                     if (tmp.isNil() || (level >= 0 && stack.realLength / 2 >= level)) {
                         result.append(elt);
                     } else {

gistfile1.txt

before
bin/jruby --dev -e "require 'active_support/all'; p ActiveSupport"  10.14s user 0.40s system 176% cpu 5.980 total
bin/jruby --dev -e "require 'active_support/all'; p ActiveSupport"  9.87s user 0.28s system 187% cpu 5.415 total
bin/jruby --dev -e "require 'active_support/all'; p ActiveSupport"  10.46s user 0.36s system 185% cpu 5.848 total
bin/jruby --dev -e "require 'active_support/all'; p ActiveSupport"  9.92s user 0.31s system 186% cpu 5.474 total

after
bin/jruby --dev -e "require 'active_support/all'; p ActiveSupport"  8.89s user 0.28s system 186% cpu 4.922 total
bin/jruby --dev -e "require 'active_support/all'; p ActiveSupport"  8.68s user 0.26s system 183% cpu 4.866 total
bin/jruby --dev -e "require 'active_support/all'; p ActiveSupport"  9.61s user 0.35s system 188% cpu 5.286 total
bin/jruby --dev -e "require 'active_support/all'; p ActiveSupport"  9.70s user 0.30s system 187% cpu 5.338 total