diff --git a/grow/definition.go b/grow/definition.go
index 543c1de..93f8d53 100644
--- a/grow/definition.go
+++ b/grow/definition.go
@@ -48,7 +48,7 @@ func (def *Definition) Grow(statusChan chan<- Status) (*vm.Program, error) {
 	for {
 		status.Attempts++
 
-		Mutate(prog)
+		Mutate(def, prog)
 
 		score, err := def.score(prog)
 		if err != nil {
@@ -58,7 +58,7 @@ func (def *Definition) Grow(statusChan chan<- Status) (*vm.Program, error) {
 
 		if score > status.BestScore {
 			status.BestScore = score
-			status.BestProgram = prog
+			status.BestProgram = prog.Copy()
 
 			if statusChan != nil {
 				statusChan <- status
@@ -73,6 +73,7 @@ func (def *Definition) Grow(statusChan chan<- Status) (*vm.Program, error) {
 
 					return nil, err
 				}
+				status.BestProgram = prog.Copy()
 
 				if statusChan != nil {
 					statusChan <- status
@@ -142,6 +143,7 @@ func (def *Definition) minifyFunction(prog *vm.Program, f int) error {
 
 		for i := 0; i < len(prog.Functions[f].Instructions); i++ {
 			origInstructions := prog.Functions[f].Instructions
+
 			tmp := make([]*vm.Instruction, len(prog.Functions[f].Instructions))
 			copy(tmp, prog.Functions[f].Instructions)
 			prog.Functions[f].Instructions = append(tmp[:i], tmp[i+1:]...)
diff --git a/grow/mutate.go b/grow/mutate.go
index 0111383..da713e7 100644
--- a/grow/mutate.go
+++ b/grow/mutate.go
@@ -8,8 +8,14 @@ import "github.com/firestuff/subcoding/vm"
 const instructionsPerFunctionMean = 15
 const instrucitonsPerFunctionStdDev = 10
 
-func Mutate(prog *vm.Program) {
-	target := int(rand.NormFloat64()*instrucitonsPerFunctionStdDev+instructionsPerFunctionMean)
+const minifyPeriodMean = 10000
+
+func Mutate(def *Definition, prog *vm.Program) {
+	if rand.Intn(minifyPeriodMean) == 0 {
+		def.minifyProgram(prog) // ignore error
+	}
+
+	target := int(rand.NormFloat64()*instrucitonsPerFunctionStdDev + instructionsPerFunctionMean)
 
 	if len(prog.Functions[0].Instructions) < target {
 		addInstruction(prog, prog.Functions[0])
diff --git a/vm/function.go b/vm/function.go
index 74b1dd2..f10c48f 100644
--- a/vm/function.go
+++ b/vm/function.go
@@ -3,3 +3,13 @@ package vm
 type Function struct {
 	Instructions []*Instruction
 }
+
+func (fnc *Function) Copy() *Function {
+	ret := &Function{}
+
+	for _, instr := range fnc.Instructions {
+		ret.Instructions = append(ret.Instructions, instr.Copy())
+	}
+
+	return ret
+}
diff --git a/vm/instruction.go b/vm/instruction.go
index 3d6129f..e1e1ecb 100644
--- a/vm/instruction.go
+++ b/vm/instruction.go
@@ -7,3 +7,15 @@ type Instruction struct {
 
 	opHandler opHandler `struc:"skip"`
 }
+
+func (instr *Instruction) Copy() *Instruction {
+	ret := &Instruction{
+		OpCode: instr.OpCode,
+	}
+
+	for i, opr := range instr.Operands {
+		ret.Operands[i] = opr.Copy()
+	}
+
+	return ret
+}
diff --git a/vm/operand.go b/vm/operand.go
index fa6546d..64e2b76 100644
--- a/vm/operand.go
+++ b/vm/operand.go
@@ -13,3 +13,14 @@ type Operand struct {
 	Reserved [3]byte
 	Value    uint64
 }
+
+func (opr *Operand) Copy() *Operand {
+	if opr == nil {
+		return nil
+	}
+
+	return &Operand{
+		Type:  opr.Type,
+		Value: opr.Value,
+	}
+}
diff --git a/vm/program.go b/vm/program.go
index f06eb47..a355c15 100644
--- a/vm/program.go
+++ b/vm/program.go
@@ -6,3 +6,17 @@ type Program struct {
 	InstructionLimit   uint64
 	Functions          []*Function
 }
+
+func (prog *Program) Copy() *Program {
+	ret := &Program{
+		GlobalMemorySize:   prog.GlobalMemorySize,
+		FunctionMemorySize: prog.FunctionMemorySize,
+		InstructionLimit:   prog.InstructionLimit,
+	}
+
+	for _, fnc := range prog.Functions {
+		ret.Functions = append(ret.Functions, fnc.Copy())
+	}
+
+	return ret
+}