bevyengine/bevy · error · EntityComponentError::AliasedMutability

The component with ID {0:?} was requested mutably more than

Error message

The component with ID {0:?} was requested mutably more than once.

What it means

EntityComponentError::AliasedMutability: a dynamic component fetch asked for mutable access to the same ComponentId more than once in one call, which would create aliasing &mut references.

Source

Thrown at crates/bevy_ecs/src/world/error.rs:45

    /// The bundles' type name.
    pub bundle_type: DebugName,
    /// The IDs of the provided entities that do not exist.
    pub entities: Vec<Entity>,
}

/// An error that occurs when a specified [`Entity`] could not be despawned.
#[derive(thiserror::Error, Debug, Clone, Copy)]
#[error("Could not despawn entity: {0}")]
pub struct EntityDespawnError(#[from] pub EntityNotSpawnedError);

/// An error that occurs when dynamically retrieving components from an entity.
#[derive(thiserror::Error, Debug, Clone, Copy, PartialEq, Eq)]
pub enum EntityComponentError {
    /// The component with the given [`ComponentId`] does not exist on the entity.
    #[error("The component with ID {0:?} does not exist on the entity.")]
    MissingComponent(ComponentId),
    /// The component with the given [`ComponentId`] was requested mutably more than once.
    #[error("The component with ID {0:?} was requested mutably more than once.")]
    AliasedMutability(ComponentId),
}

/// An error that occurs when fetching entities mutably from a world.
#[derive(thiserror::Error, Debug, Clone, Copy, PartialEq, Eq)]
pub enum EntityMutableFetchError {
    /// The entity is not spawned.
    #[error(
        "{0}\n
    If you were attempting to apply a command to this entity,
    and want to handle this error gracefully, consider using `EntityCommands::queue_handled` or `queue_silenced`."
    )]
    NotSpawned(#[from] EntityNotSpawnedError),
    /// The entity with the given ID was requested mutably more than once.
    #[error("The entity with ID {0} was requested mutably more than once")]
    AliasedMutability(Entity),
}

View on GitHub (pinned to 396ca72708)

Solutions

1. Request each component mutably only once per fetch
2. Split the mutation into separate sequential operations
3. Use the read-only fetch for the duplicate access

When it happens

Trigger: Thrown at crates/bevy_ecs/src/world/error.rs:45 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/ba558dc521a3a3c7. Report an issue: GitHub.