diff --git a/twasm/asm/main.asm b/twasm/asm/main.asm
index 239e0d5..c371189 100644
--- a/twasm/asm/main.asm
+++ b/twasm/asm/main.asm
@@ -1302,6 +1302,7 @@ get_opcode:
   .found:
     shl eax, 4
     mov dl, [esi + 8 + opcodes.by_id + eax]
+    and edx, 0xFF
     mov al, [esi + 2 + opcodes.by_id + eax]
     and eax, 0xFF
     ret