diff --git a/vm.cpp b/vm.cpp
index e6025ad..0c8b369 100644
--- a/vm.cpp
+++ b/vm.cpp
@@ -79,6 +79,7 @@ enum OPS {
 
 	OP_IN,
 	OP_OUT,
+	OP_SLEEP,
 };
 
 typedef void(*t_extcall)(t_stack&);
@@ -99,6 +100,7 @@ t_stack vm_callstack;
 unsigned short rX = 0;
 unsigned char rY = 0;
 unsigned char rZ = 0;
+bool sleeping = false;
 
 
 static void load_rom() {
@@ -133,6 +135,8 @@ void vm_init(const char* filename) {
 inline unsigned short WORD() { vm_pc += 2; return vm_program[vm_pc - 2] + (vm_program[vm_pc - 1] << 8); }
 
 const int vm_step() {
+	if (sleeping) return vm_cycles;
+
 	char val, val2;
 	switch (vm_program[vm_pc++]) {
 
@@ -204,6 +208,7 @@ const int vm_step() {
 	case OP_GEQ: stack_push(vm_datastack, stack_pop(vm_datastack) >= stack_pop(vm_datastack)); vm_cycles++; break;
 	case OP_IN: stack_push(vm_datastack, in_ports[vm_program[vm_pc++]]()); vm_cycles++; break;
 	case OP_OUT: out_ports[vm_program[vm_pc++]](stack_pop(vm_datastack)); vm_cycles++; break;
+	case OP_SLEEP: sleeping = true; vm_cycles++; break;
 	}
 	return vm_cycles;
 }
@@ -221,6 +226,7 @@ void vm_register_out_port(const byte port, t_out_port callback) {
 }
 
 void vm_call_interrupt(const char num) {
+	sleeping = false;
 	stack_push(vm_callstack, vm_pc);
 	stack_push(vm_callstack, rX & 255);
 	stack_push(vm_callstack, rX >> 8);