diff --git a/libs/sysjs/src/mach-sysjs.js b/libs/sysjs/src/mach-sysjs.js
index 8c742f43..fd177130 100644
--- a/libs/sysjs/src/mach-sysjs.js
+++ b/libs/sysjs/src/mach-sysjs.js
@@ -40,6 +40,10 @@ class MemoryBlock {
     return this.getMemory().getFloat64(offset, true);
   }
 
+  getSlice(offset, len) {
+    return new Uint8Array(this.mem, offset, len);
+  }
+
   getString(offset, len) {
     return text_decoder.decode(new Uint8Array(this.mem, offset, len));
   }
@@ -252,6 +256,16 @@ const zig = {
     delete values[id][index];
   },
 
+  zigCopyBytes(id, bytes, expected_length) {
+    let memory = new MemoryBlock(zig.wasm.exports.memory.buffer);
+    const array = values[id];
+    if (array.length != expected_length) {
+      throw Error("copyBytes given array of length " + expected_length + " but destination has length " + array.length);
+    }
+    const slice = memory.getSlice(bytes, array.length);
+    array.set(slice);
+  },
+
   zigGetAttributeCount(id) {
     let obj = values[id];
     return Object.keys(obj).length;
diff --git a/libs/sysjs/src/main.zig b/libs/sysjs/src/main.zig
index eafb75d5..77b4747e 100644
--- a/libs/sysjs/src/main.zig
+++ b/libs/sysjs/src/main.zig
@@ -18,6 +18,7 @@ const js = struct {
     extern fn zigValueEqual(val: *const anyopaque, other: *const anyopaque) bool;
     extern fn zigValueInstanceOf(val: *const anyopaque, other: *const anyopaque) bool;
     extern fn zigDeleteIndex(id: u64, index: u32) void;
+    extern fn zigCopyBytes(id: u64, bytes: [*]u8, expected_len: u32) void;
     extern fn zigFunctionCall(id: u64, name: [*]const u8, len: u32, args: ?*const anyopaque, args_len: u32, ret_ptr: *anyopaque) void;
     extern fn zigFunctionInvoke(id: u64, args: ?*const anyopaque, args_len: u32, ret_ptr: *anyopaque) void;
     extern fn zigGetParamCount(id: u64) u32;
@@ -140,6 +141,10 @@ pub const Object = struct {
         js.zigDeleteIndex(obj.ref, index);
     }
 
+    pub fn copyBytes(obj: *const Object, bytes: []u8) void {
+        js.zigCopyBytes(obj.ref, bytes.ptr, bytes.len);
+    }
+
     pub fn call(obj: *const Object, fun: []const u8, args: []const Value) Value {
         var ret: Value = undefined;
         js.zigFunctionCall(obj.ref, fun.ptr, @intCast(u32, fun.len), args.ptr, @intCast(u32, args.len), &ret);