diff --git a/creature.go b/creature.go
index 8880828..a90ef03 100644
--- a/creature.go
+++ b/creature.go
@@ -11,10 +11,7 @@ type Word interface {
 // data, and provides methods to run this program data, as well as interact with
 // it.
 type Machine [WORD Word] struct {
-	// Program is not modified by the machine, and can be freely set before
-	// the machine is started.
-	Program []WORD
-
+	program   []WORD
 	stack     []WORD
 	block     []WORD
 	counter   WORD
@@ -87,7 +84,7 @@ func (machine *Machine[WORD]) Reset() {
 func (machine *Machine[WORD]) Execute(offset WORD) (err error) {
 	machine.counter = offset
 
-	for int(machine.counter) < len(machine.Program) {
+	for int(machine.counter) < len(machine.program) {
 		switch machine.instruction() {
 		case PUSH:
 			machine.counter++
@@ -202,7 +199,7 @@ func (machine *Machine[WORD]) Execute(offset WORD) (err error) {
 
 // Instruction returns the current instruction in program memory.
 func (machine *Machine[WORD]) instruction() (instruction WORD) {
-	instruction = machine.Program[machine.counter]
+	instruction = machine.program[machine.counter]
 	return
 }
 
@@ -291,6 +288,12 @@ func (machine *Machine[WORD]) Unregister(id WORD) {
 	delete(machine.functions, id)
 }
 
+// LoadProgram loads the contents of program into the machine's program memory.
+func (machine *Machine[WORD]) LoadProgram(program []WORD) {
+	machine.program = make([]WORD, len(program))
+	copy(machine.program, program)
+}
+
 // LoadMemory loads the contents of block into the machine's memory.
 func (machine *Machine[WORD]) LoadMemory(block []WORD) {
 	machine.block = make([]WORD, len(block))
diff --git a/creature_test.go b/creature_test.go
index a320dad..9a54bbd 100644
--- a/creature_test.go
+++ b/creature_test.go
@@ -9,7 +9,8 @@ func runMachineTest (
 ) (
 	machine *Machine[int],
 ) {
-	machine = &Machine[int] { Program: program }
+	machine = &Machine[int] {}
+	machine.LoadProgram(program)
 	if memory != nil {
 		machine.LoadMemory(memory)
 	}
@@ -230,7 +231,8 @@ func TestJump(test *testing.T) {
 
 func TestRegister(test *testing.T) {
 	output := ""
-	machine := &Machine[int] { Program: []int {
+	machine := &Machine[int] {}
+	machine.LoadProgram([]int {
 		PUSH, int('h'),
 		PUSH, 4,
 		CAL,
@@ -258,7 +260,7 @@ func TestRegister(test *testing.T) {
 		PUSH, int('!'),
 		PUSH, 4,
 		CAL,
-	}}
+	})
 	machine.Register(4, func(machine *Machine[int]) (stop bool) {
 		output += string(rune(machine.Pop()))
 		return
diff --git a/examples/echo.go b/examples/echo.go
index 8a3d8ba..c5ff5a1 100644
--- a/examples/echo.go
+++ b/examples/echo.go
@@ -9,7 +9,8 @@ func main () {
 	// this is a simple echo program. it will take in input indefinetly and
 	// repeat it. due to line buffering in the terminal however, it will
 	// only print output once you have pressed enter.
-	machine := cre.Machine[int] { Program: []int {
+	machine := cre.Machine[int] {}
+	machine.LoadProgram([]int {
 		cre.PUSH, 0,
 		cre.CAL,
 
@@ -19,7 +20,7 @@ func main () {
 		cre.PUSH, 1,
 		cre.PUSH, 0,
 		cre.JMP,
-	}}
+	})
 
 	machine.Register (0, read)
 	machine.Register (1, write)
diff --git a/examples/psychiatrist.go b/examples/psychiatrist.go
index 72338b5..f3e4ec9 100644
--- a/examples/psychiatrist.go
+++ b/examples/psychiatrist.go
@@ -20,7 +20,8 @@ func main () {
 	responseStart     := 71
 	responseLoopStart := 50
 	
-	machine := cre.Machine[int] { Program: []int {
+	machine := cre.Machine[int] {}
+	machine.LoadProgram([]int {
 		// reset x
 		cre.PUSH, introStart,
 		cre.PUSH, x,
@@ -108,7 +109,7 @@ func main () {
 		cre.PUSH, 1,
 		cre.PUSH, responseLoopStart,
 		cre.JMP,
-	}}
+	})
 
 	stringData := []byte (
 		"\x00" +