diff --git a/src/server/services/stepConverter.ts b/src/server/services/stepConverter.ts
index 40347fc..133d330 100644
--- a/src/server/services/stepConverter.ts
+++ b/src/server/services/stepConverter.ts
@@ -53,9 +53,11 @@ export async function convertStepFile(
     sourceFile: path.basename(inputPath),
     meshCount:  result.meshes.length,
     meshes: result.meshes.map(mesh => {
-      const pos = mesh.attributes.position.array
-      const nor = mesh.attributes.normal?.array
-      const idx = mesh.index.array
+      // Explicitly wrap in typed arrays — WASM may return array-like objects
+      // without a .buffer property, which would break Buffer.from().
+      const pos = new Float32Array(mesh.attributes.position.array)
+      const nor = mesh.attributes.normal ? new Float32Array(mesh.attributes.normal.array) : null
+      const idx = new Uint32Array(mesh.index.array)
       return {
         positions: Buffer.from(pos.buffer, pos.byteOffset, pos.byteLength).toString('base64'),
         normals:   nor ? Buffer.from(nor.buffer, nor.byteOffset, nor.byteLength).toString('base64') : null,