diff --git a/wgpu/src/backend/custom.rs b/wgpu/src/backend/custom.rs
index a37854d7e2..dd27535198 100644
--- a/wgpu/src/backend/custom.rs
+++ b/wgpu/src/backend/custom.rs
@@ -30,7 +30,7 @@ impl DynContext {
     }
 
     #[cfg(webgpu)]
-    pub fn from_webgpu(instance: super::ContextWebGpu) -> Self {
+    pub(crate) fn from_webgpu(instance: super::ContextWebGpu) -> Self {
         Self(Arc::new(instance))
     }
 }
@@ -324,6 +324,16 @@ impl QueueInterface for DynQueue {
     fn on_submitted_work_done(&self, callback: dispatch::BoxSubmittedWorkDoneCallback) {
         self.0.on_submitted_work_done(callback);
     }
+
+    #[cfg(any(webgpu, webgl))]
+    fn copy_external_image_to_texture(
+        &self,
+        _source: &wgt::CopyExternalImageSourceInfo,
+        _dest: wgt::CopyExternalImageDestInfo<&crate::api::Texture>,
+        _size: crate::Extent3d,
+    ) {
+        unimplemented!()
+    }
 }
 
 #[derive(Debug)]
@@ -388,6 +398,14 @@ impl BufferInterface for DynBuffer {
     fn destroy(&self) {
         self.0.destroy();
     }
+
+    #[cfg(webgpu)]
+    fn get_mapped_range_as_array_buffer(
+        &self,
+        _sub_range: Range<wgt::BufferAddress>,
+    ) -> Option<js_sys::ArrayBuffer> {
+        unimplemented!()
+    }
 }
 
 #[derive(Debug)]