diff --git a/tool/lib/core_assertions.rb b/tool/lib/core_assertions.rb
index 723a1742c5..67373139ca 100644
--- a/tool/lib/core_assertions.rb
+++ b/tool/lib/core_assertions.rb
@@ -3,6 +3,10 @@
 module Test
   module Unit
     module Assertions
+      def assert_raises(*exp, &b)
+        raise NoMethodError, "use assert_raise", caller
+      end
+
       def _assertions= n # :nodoc:
         @_assertions = n
       end
diff --git a/tool/lib/test/unit/assertions.rb b/tool/lib/test/unit/assertions.rb
index 3244913a36..b4f1dbc176 100644
--- a/tool/lib/test/unit/assertions.rb
+++ b/tool/lib/test/unit/assertions.rb
@@ -563,10 +563,6 @@ module Test
         assert yield, *msgs
       end
 
-      def assert_raises(*exp, &b)
-        raise NoMethodError, "use assert_raise", caller
-      end
-
       # :call-seq:
       #   assert_nothing_thrown( failure_message = nil, &block )
       #