diff --git a/include/fc/variant_object.hpp b/include/fc/variant_object.hpp
index 32d8e83..b2f2e4e 100644
--- a/include/fc/variant_object.hpp
+++ b/include/fc/variant_object.hpp
@@ -59,7 +59,7 @@ namespace fc
       const variant& operator[]( const string& key )const;
       const variant& operator[]( const char* key )const;
       size_t size()const;
-      bool   contains( const char* key ) { return find(key) != end(); }
+      bool   contains( const char* key ) const { return find(key) != end(); }
       ///@}
 
       variant_object();