diff --git a/src/uxn.zig b/src/uxn.zig
index 0e230c1..c7d38db 100644
--- a/src/uxn.zig
+++ b/src/uxn.zig
@@ -683,29 +683,66 @@ fn sft(stack: *Stack, comptime T: type, comptime keep: bool) void {
     }
 }
 
+// Adaptation of https://git.sr.ht/~rabbits/uxn-utils/tree/096fb78a781dcb0454083c3eda89298b98a5187f/item/cli/opctest/src/opctest.tal
+//
+// MIT License
+//
+// Copyright (c) Devine Lu Linvega
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
 test "op" {
     var uxn = try Uxn.init(std.testing.allocator);
     defer uxn.deinit(std.testing.allocator);
 
     const rom = [_]u8{
         0x01, 0x01, 0x01, 0x01,
+        0x21, 0x21, 0x21, 0x21,
         0x00,
     };
     @memcpy(uxn.mem.m[0x100 .. rom.len + 0x100], &rom);
 
     std.debug.print("op.inc\n", .{});
-    uxn.ws.push(u8, 0x01);
-    uxn.ws.push(u8, 0xff);
-    uxn.ws.push(u8, 0xfe);
+    uxn.ws.push(u16, 0x0000);
+    uxn.ws.push(u16, 0xfffe);
+    uxn.ws.push(u16, 0xffff);
+    uxn.ws.push(u16, 0x0001);
     uxn.ws.push(u8, 0x00);
+    uxn.ws.push(u8, 0xfe);
+    uxn.ws.push(u8, 0xff);
+    uxn.ws.push(u8, 0x01);
     _ = uxn.eval();
-    try std.testing.expectEqual(0x01, uxn.ws.pop(u8));
-    _ = uxn.eval();
-    try std.testing.expectEqual(0xff, uxn.ws.pop(u8));
+    try std.testing.expectEqual(0x02, uxn.ws.pop(u8));
     _ = uxn.eval();
     try std.testing.expectEqual(0x00, uxn.ws.pop(u8));
     _ = uxn.eval();
-    try std.testing.expectEqual(0x02, uxn.ws.pop(u8));
+    try std.testing.expectEqual(0xff, uxn.ws.pop(u8));
+    _ = uxn.eval();
+    try std.testing.expectEqual(0x01, uxn.ws.pop(u8));
+    _ = uxn.eval();
+    try std.testing.expectEqual(0x0002, uxn.ws.pop(u16));
+    _ = uxn.eval();
+    try std.testing.expectEqual(0x0000, uxn.ws.pop(u16));
+    _ = uxn.eval();
+    try std.testing.expectEqual(0xffff, uxn.ws.pop(u16));
+    _ = uxn.eval();
+    try std.testing.expectEqual(0x0001, uxn.ws.pop(u16));
 }
 
 pub fn formatInstruction(