diff --git a/lib-topaz/bootstrap.rb b/lib-topaz/bootstrap.rb
index 7601773d1..f38819736 100644
--- a/lib-topaz/bootstrap.rb
+++ b/lib-topaz/bootstrap.rb
@@ -5,6 +5,7 @@
   load(File.join(lib_topaz, file))
 end
 
+load_bootstrap.call("thread.rb")
 load_bootstrap.call("array.rb")
 load_bootstrap.call("class.rb")
 load_bootstrap.call("comparable.rb")
diff --git a/lib-topaz/thread.rb b/lib-topaz/thread.rb
new file mode 100644
index 000000000..81a99eefe
--- /dev/null
+++ b/lib-topaz/thread.rb
@@ -0,0 +1,26 @@
+class Thread
+  def recursion_guard_outer(identifier, obj, &block)
+    # We want to throw something less likely to be caught accidentally outside
+    # our own code than the recursion identifier. Ideally this should be an
+    # object that is unique to this particular recursion guard. Since doing
+    # that properly requires pushing extra state all the way up into
+    # ExecutionContext, we do this instead.
+    throw_symbol = "__recursion_guard_#{identifier}".to_sym
+
+    if self.in_recursion_guard?(identifier)
+      self.recursion_guard(identifier, obj) do
+        yield
+        return false
+      end
+      throw(throw_symbol)
+    else
+      self.recursion_guard(identifier, obj) do
+        catch(throw_symbol) do
+          yield
+          return false
+        end
+        return true
+      end
+    end
+  end
+end
diff --git a/tests/objects/test_threadobject.py b/tests/objects/test_threadobject.py
index 64724c196..1179bb167 100644
--- a/tests/objects/test_threadobject.py
+++ b/tests/objects/test_threadobject.py
@@ -56,3 +56,18 @@ def bar(objs, depth)
         w_depth, w_symbol = space.listview(w_res)
         assert space.int_w(w_depth) == 5
         assert space.symbol_w(w_symbol) == "a"
+
+    def test_recursion_guard_outer(self, space):
+        w_res = space.execute("""
+        def foo(objs, depth = 0)
+          obj = objs.shift
+          Thread.current.recursion_guard_outer(:foo, obj) do
+            return foo(objs, depth + 1)
+          end
+          return [depth, obj]
+        end
+        return foo([:a, :b, :c, :a, :d])
+        """)
+        w_depth, w_symbol = space.listview(w_res)
+        assert space.int_w(w_depth) == 0
+        assert space.symbol_w(w_symbol) == "a"
diff --git a/topaz/objects/threadobject.py b/topaz/objects/threadobject.py
index d7e3301cb..45e89ff73 100644
--- a/topaz/objects/threadobject.py
+++ b/topaz/objects/threadobject.py
@@ -42,3 +42,11 @@ def method_recursion_guard(self, space, w_identifier, w_obj, block):
             if not in_recursion:
                 space.invoke_block(block, [])
             return space.newbool(in_recursion)
+
+    @classdef.method("in_recursion_guard?")
+    def method_in_recursion_guardp(self, space, w_identifier):
+        ec = space.getexecutioncontext()
+        identifier = space.str_w(w_identifier)
+        if identifier in ec.recursive_calls:
+            return space.w_true
+        return space.w_false