diff --git a/src/Runtime.zig b/src/Runtime.zig
index 29b749e..4eeafd0 100644
--- a/src/Runtime.zig
+++ b/src/Runtime.zig
@@ -253,7 +253,7 @@ pub fn populatePushConstants(self: *Self, blob: []const u8) RuntimeError!void {
 
 pub fn writeDescriptorSet(self: *const Self, input: []const u8, set: SpvWord, binding: SpvWord, descriptor_index: SpvWord) RuntimeError!void {
     if (set < lib.SPIRV_MAX_SET and binding < lib.SPIRV_MAX_SET_BINDINGS) {
-        const value = &self.results[self.mod.bindings[set][binding]].variant.?.Variable.value;
+        const value = &(self.results[self.mod.bindings[set][binding]].variant orelse return).Variable.value;
         switch (value.*) {
             .Array => |arr| {
                 if (descriptor_index >= arr.values.len)
diff --git a/src/Value.zig b/src/Value.zig
index 40237ac..259e618 100644
--- a/src/Value.zig
+++ b/src/Value.zig
@@ -103,6 +103,7 @@ pub const Value = union(Type) {
         }
     },
     Structure: struct {
+        external_data: ?[]u8,
         offsets: []const ?SpvWord,
         values: []Self,
     },
@@ -217,6 +218,7 @@ pub const Value = union(Type) {
                 .Structure => |s| blk: {
                     const self: Self = .{
                         .Structure = .{
+                            .external_data = null,
                             .offsets = allocator.dupe(?SpvWord, s.members_offsets) catch return RuntimeError.OutOfMemory,
                             .values = allocator.alloc(Self, member_count) catch return RuntimeError.OutOfMemory,
                         },
@@ -290,6 +292,7 @@ pub const Value = union(Type) {
                     errdefer allocator.free(values);
                     for (values, s.values) |*new_value, value| new_value.* = try value.dupe(allocator);
                     break :blk .{
+                        .external_data = s.external_data,
                         .offsets = allocator.dupe(?SpvWord, s.offsets) catch return RuntimeError.OutOfMemory,
                         .values = values,
                     };
@@ -429,6 +432,7 @@ pub const Value = union(Type) {
                 }
                 return end_offset;
             },
+            .RuntimeArray => {},
             else => return RuntimeError.InvalidValueType,
         }
         return 0;
@@ -559,13 +563,14 @@ pub const Value = union(Type) {
                 }
                 return offset;
             },
-            .Structure => |s| {
+            .Structure => |*s| {
                 var end_offset: usize = 0;
                 for (s.values, 0..) |*v, i| {
                     const member_offset: usize = @intCast(s.offsets[i] orelse end_offset);
                     const write_size = try v.write(input[member_offset..]);
                     end_offset = @max(end_offset, member_offset + write_size);
                 }
+                s.external_data = input[0..end_offset];
                 return end_offset;
             },
             .RuntimeArray => |*arr| arr.data = input[0..],
@@ -649,15 +654,15 @@ pub const Value = union(Type) {
                         },
                         .f32_ptr => |ptr| {
                             if (window.len < @sizeOf(f32)) return RuntimeError.OutOfBounds;
-                            std.mem.copyForwards(u8, window[0..@sizeOf(f32)], std.mem.asBytes(ptr));
+                            @memcpy(window[0..@sizeOf(f32)], std.mem.asBytes(ptr));
                         },
                         .i32_ptr => |ptr| {
                             if (window.len < @sizeOf(i32)) return RuntimeError.OutOfBounds;
-                            std.mem.copyForwards(u8, window[0..@sizeOf(i32)], std.mem.asBytes(ptr));
+                            @memcpy(window[0..@sizeOf(i32)], std.mem.asBytes(ptr));
                         },
                         .u32_ptr => |ptr| {
                             if (window.len < @sizeOf(u32)) return RuntimeError.OutOfBounds;
-                            std.mem.copyForwards(u8, window[0..@sizeOf(u32)], std.mem.asBytes(ptr));
+                            @memcpy(window[0..@sizeOf(u32)], std.mem.asBytes(ptr));
                         },
                     }
 
diff --git a/src/opcodes.zig b/src/opcodes.zig
index efb60ee..a575d5d 100644
--- a/src/opcodes.zig
+++ b/src/opcodes.zig
@@ -1452,7 +1452,13 @@ fn opAccessChain(allocator: std.mem.Allocator, word_count: SpvWord, rt: *Runtime
                                         end_offset = @max(end_offset, field_offset + try field.getPlainMemorySize());
                                     }
                                     const member_offset: usize = @intCast(s.offsets[component_index] orelse end_offset);
-                                    uniform_slice_window = try helpers.advanceWindow(uniform_slice_window, member_offset);
+
+                                    if (uniform_slice_window != null) {
+                                        uniform_slice_window = try helpers.advanceWindow(uniform_slice_window, member_offset);
+                                    } else if (s.external_data) |data| {
+                                        uniform_slice_window = data[0..];
+                                    }
+
                                     value_ptr = &s.values[component_index];
                                 },
                                 .RuntimeArray => |*arr| {