diff --git a/src/webgpu/util/unions.ts b/src/webgpu/util/unions.ts
index d105afb64789..23381ddee9d5 100644
--- a/src/webgpu/util/unions.ts
+++ b/src/webgpu/util/unions.ts
@@ -1,13 +1,39 @@
+/**
+ * Reifies a `GPUOrigin3D` into a `Required<GPUOrigin3DDict>`.
+ */
+export function reifyOrigin3D(
+  val: Readonly<GPUOrigin3DDict> | Iterable<number>
+): Required<GPUOrigin3DDict> {
+  if (Symbol.iterator in val) {
+    const v = Array.from(val as Iterable<number>);
+    return {
+      x: v[0] ?? 0,
+      y: v[1] ?? 0,
+      z: v[2] ?? 0,
+    };
+  } else {
+    const v = val as Readonly<GPUOrigin3DDict>;
+    return {
+      x: v.x ?? 0,
+      y: v.y ?? 0,
+      z: v.z ?? 0,
+    };
+  }
+}
+
 /**
  * Reifies a `GPUExtent3D` into a `Required<GPUExtent3DDict>`.
  */
 export function reifyExtent3D(
   val: Readonly<GPUExtent3DDict> | Iterable<number>
 ): Required<GPUExtent3DDict> {
-  // TypeScript doesn't seem to want to narrow the types here properly, so hack around it.
-  if (typeof (val as Iterable<number>)[Symbol.iterator] === 'function') {
+  if (Symbol.iterator in val) {
     const v = Array.from(val as Iterable<number>);
-    return { width: v[0] ?? 1, height: v[1] ?? 1, depthOrArrayLayers: v[2] ?? 1 };
+    return {
+      width: v[0] ?? 1,
+      height: v[1] ?? 1,
+      depthOrArrayLayers: v[2] ?? 1,
+    };
   } else {
     const v = val as Readonly<GPUExtent3DDict>;
     return {