Method and apparatus for managing access to registers that are outside a current register stack frame are disclosed. An instruction execution unit in a processor receives an instruction to be executed. A processor includes a register stack, the register stack including a plurality of register stack frames. Each of the register stack frames includes zero or more registers. One of the plurality of register stack frames is a current register stack frame. When execution of the instruction requires writing to a register referenced by the instruction, the instruction execution unit determines whether the register referenced by the instruction is within the current register stack frame. If the instruction execution unit determines that the register is not within the current register stack frame, the instruction execution unit does not execute the instruction and may, for example, generate a fault. The instruction execution unit executes the instruction is the instruction execution unit determines that the register is within the current register stack frame. When execution of the instruction requires reading from a register referenced by the instruction, the instruction execution unit executes the instruction whether or not the register referenced by the instruction is within the current register stack frame.