1 files changed, 2 insertions, 1 deletions
diff --git a/lib/ostruct.rb b/lib/ostruct.rb
index 8cf1233a79..67ba043535 100644
--- a/lib/ostruct.rb
+++ b/lib/ostruct.rb
@@ -156,7 +156,8 @@ class OpenStruct
     begin
       @modifiable = true
     rescue
-      raise FrozenError, "can't modify frozen #{self.class}", caller(3)
+      exception_class = defined?(FrozenError) ? FrozenError : RuntimeError
+      raise exception_class, "can't modify frozen #{self.class}", caller(3)
     end
     @table
   end