diff --git a/lib/json_logic.rb b/lib/json_logic.rb
index 3bb256b..1a3c8a2 100644
--- a/lib/json_logic.rb
+++ b/lib/json_logic.rb
@@ -12,7 +12,7 @@ def self.apply(logic, data)
       # Pass-thru
       logic
     else
-      if data.is_a?(Hash)
+      if data.is_a?(Hash) && data.keys.any?(Symbol)
         data = data.stringify_keys
       end
       data ||= {}