bevyengine/bevy · error

B0002

B0002

Error message

error[B0002]: Res<{}> in system {} conflicts with a previous system parameter. Consider removing the duplicate access using `Without<IsResource>` to create disjoint Queries or merging conflicting Queries into a `ParamSet`. See: https://bevy.org/learn/errors/b0002

What it means

Error "error[B0002]: Res<{}> in system {} conflicts with a previous system parameter. Consider removing the duplicate access using `Without<IsResource>` to create disjoint Queries or merging conflicting Queries into a `ParamSet`. See: https://bevy.org/learn/errors/b0002" thrown in bevyengine/bevy.

Source

Thrown at crates/bevy_ecs/src/system/system_param.rs:701

        component_access_set: &mut FilteredAccessSet,
        world: &mut World,
    ) {
        let mut filter = FilteredAccess::default();
        filter.add_read(component_id);
        filter.and_with(IS_RESOURCE);

        let conflicts = component_access_set.get_conflicts_single(&filter);
        if conflicts.is_empty() {
            component_access_set.add(filter);
            return;
        }

        let mut accesses = conflicts.format_conflict_list(world.as_unsafe_world_cell());
        // Access list may be empty (if access to all components requested)
        if !accesses.is_empty() {
            accesses.push(' ');
        }
        panic!("error[B0002]: Res<{}> in system {} conflicts with a previous system parameter. Consider removing the duplicate access using `Without<IsResource>` to create disjoint Queries or merging conflicting Queries into a `ParamSet`. See: https://bevy.org/learn/errors/b0002", DebugName::type_name::<T>(), system_meta.name);
    }

    #[inline]
    unsafe fn get_param<'w, 's>(
        &mut component_id: &'s mut Self::State,
        system_meta: &SystemMeta,
        world: UnsafeWorldCell<'w>,
        change_tick: Tick,
    ) -> Result<Self::Item<'w, 's>, SystemParamValidationError> {
        let (ptr, ticks) = world.get_resource_with_ticks(component_id).ok_or_else(|| {
            SystemParamValidationError::invalid::<Self>("Resource does not exist")
        })?;
        Ok(Res {
            value: ptr.deref(),
            ticks: ComponentTicksRef {
                added: ticks.added.deref(),
                changed: ticks.changed.deref(),
                changed_by: ticks.changed_by.map(|changed_by| changed_by.deref()),

View on GitHub (pinned to 396ca72708)

Solutions

1. Remove the duplicate Res<T> parameter or the conflicting mutable access from the system signature
2. Wrap conflicting accesses in a ParamSet<T0, T1, ...>
3. If the conflict is with a query, add Without<IsResource> or a disjoint component filter to the query
4. Split the system into two systems with disjoint access and order them explicitly

When it happens

Trigger: Thrown at crates/bevy_ecs/src/system/system_param.rs:701 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of bevyengine/bevy@396ca72708 (2026-08-20). Data as JSON: /api/errors/b43b11b22326c60b. Report an issue: GitHub.