diff --git a/libs/ecs/include/psemek/ecs/detail/apply_helper.hpp b/libs/ecs/include/psemek/ecs/detail/apply_helper.hpp
index 17ba12bf..e878d7b8 100644
--- a/libs/ecs/include/psemek/ecs/detail/apply_helper.hpp
+++ b/libs/ecs/include/psemek/ecs/detail/apply_helper.hpp
@@ -43,19 +43,19 @@ namespace psemek::ecs::detail
 
 		if constexpr (std::invocable<Function, entity_container &, util::span<entity_handle const>, util::span<Components> ...>)
 		{
-			function(parent, handles_span, util::span<Components>{components, count} ...);
+			function(parent, handles_span, util::span<Components>{components, is_empty_v<Components> ? 1 : count} ...);
 		}
 		else if constexpr (std::invocable<Function, util::span<entity_handle const>, util::span<Components> ...>)
 		{
-			function(handles_span, util::span<Components>{components, count} ...);
+			function(handles_span, util::span<Components>{components, is_empty_v<Components> ? 1 : count} ...);
 		}
 		else if constexpr (std::invocable<Function, entity_container &, util::span<Components> ...>)
 		{
-			function(parent, util::span<Components>{components, count} ...);
+			function(parent, util::span<Components>{components, is_empty_v<Components> ? 1 : count} ...);
 		}
 		else
 		{
-			function(util::span<Components>{components, count} ...);
+			function(util::span<Components>{components, is_empty_v<Components> ? 1 : count} ...);
 		}
 	}
 
diff --git a/libs/ecs/include/psemek/ecs/entity_container.hpp b/libs/ecs/include/psemek/ecs/entity_container.hpp
index 8b04a3f9..4a66bf33 100644
--- a/libs/ecs/include/psemek/ecs/entity_container.hpp
+++ b/libs/ecs/include/psemek/ecs/entity_container.hpp
@@ -126,6 +126,9 @@ namespace psemek::ecs
 		 *      void(span<entity_handle const>, span<components>...)
 		 *      void(entity_container, span<components>...)
 		 *      void(entity_container, span<entity_handle const>, span<components>...)
+		 *  The size of all spans within a single function call are the same,
+		 *    except for empty component types (i.e. std::is_empty_v<Component> is true),
+		 *    each having an unspecified non-zero size.
 		 *  An optional query cache can be supplied to speed up iteration.
 		 *  If the query cache wasn't created with the exact sequence of component
 		 *    types, the behavior is undefined.