bevyengine/bevy · error

Fallback buffer should exist

Error message

Fallback buffer should exist

What it means

Panic in create_buffer_binding_resource_arrays: a bindless descriptor references a fallback buffer index that has no entry in the fallback_buffers map. Fallback buffers are created for every bindless slot at startup, so absence indicates initialization was skipped or corrupted.

Source

Thrown at crates/bevy_render/src/material_bind_groups.rs:1960

    /// Accumulates buffer binding arrays into binding resource arrays suitable
    /// for `wgpu`.
    fn create_buffer_binding_resource_arrays<'a, 'b>(
        &'a self,
        binding_resource_arrays: &'b mut Vec<(&'a u32, BindingResourceArray<'a>)>,
        fallback_buffers: &'a HashMap<BindlessIndex, Buffer>,
        shader_buffer_assets: &'a RenderAssets<GpuShaderBuffer>,
        bindless_descriptor: &'a BindlessDescriptor,
        required_binding_array_size: Option<u32>,
    ) {
        for bindless_buffer_descriptor in bindless_descriptor.buffers.iter() {
            // If this is a raw buffer, create the binding.
            if let Some(buffer_bindless_binding_array) =
                self.buffers.get(&bindless_buffer_descriptor.bindless_index)
            {
                let fallback_buffer = fallback_buffers
                    .get(&bindless_buffer_descriptor.bindless_index)
                    .expect("Fallback buffer should exist");

                let mut buffer_bindings: Vec<_> = buffer_bindless_binding_array
                    .bindings
                    .iter()
                    .map(|maybe_bindless_binding| {
                        let buffer = match *maybe_bindless_binding {
                            None => fallback_buffer,
                            Some(ref bindless_binding) => &bindless_binding.resource,
                        };
                        BufferBinding {
                            buffer,
                            offset: 0,
                            size: None,
                        }
                    })
                    .collect();

                if let Some(required_binding_array_size) = required_binding_array_size {

View on GitHub (pinned to 396ca72708)

Solutions

1. Report as a Bevy engine bug with a reproducing project
2. Avoid the buffer-heavy bindless material setup that triggers it

When it happens

Trigger: Thrown at crates/bevy_render/src/material_bind_groups.rs:1960 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/a0840b849522848f. Report an issue: GitHub.