diff --git a/libs/util/include/psemek/util/hash_table.hpp b/libs/util/include/psemek/util/hash_table.hpp
index 1c975352..389723f6 100644
--- a/libs/util/include/psemek/util/hash_table.hpp
+++ b/libs/util/include/psemek/util/hash_table.hpp
@@ -519,7 +519,7 @@ namespace psemek::util
 			impl_.clear();
 		}
 
-		bool empty()
+		bool empty() const
 		{
 			return impl_.size() == 0;
 		}
@@ -679,7 +679,7 @@ namespace psemek::util
 			return impl_.size();
 		}
 
-		bool empty()
+		bool empty() const
 		{
 			return impl_.size() == 0;
 		}