diff --git a/libs/util/include/psemek/util/dynamic_bitset.hpp b/libs/util/include/psemek/util/dynamic_bitset.hpp
index 678871cc..2c7438cd 100644
--- a/libs/util/include/psemek/util/dynamic_bitset.hpp
+++ b/libs/util/include/psemek/util/dynamic_bitset.hpp
@@ -97,7 +97,7 @@ namespace std
 	template <>
 	struct hash<::psemek::util::dynamic_bitset>
 	{
-		std::size_t operator()(::psemek::util::dynamic_bitset const & b)
+		std::size_t operator()(::psemek::util::dynamic_bitset const & b) const
 		{
 			std::size_t result = 0x23d2ef655094f9aeull;
 			for (auto value : b.storage())