Embodiments that facilitate type checking of assembly language instructions are disclosed. In one embodiment, a method includes receiving a low level language instruction in a memory. The instruction includes a word having a first type. The memory includes either a stack or a heap. Each of the stack or heap includes a plurality of positions. The method also includes labeling the plurality of positions in one of the stack or the heap as one or more specified positions and one or more unspecified positions. The method further includes assigning a second type to the memory, the second type including the first type of the word. The word is stored in a specified position or an unspecified position. The method additionally includes determining whether the instruction is well-typed by applying one or more rules to the instruction and to the second type.