diff --git a/stackframe.go b/stackframe.go
index 259eae1..006cce3 100644
--- a/stackframe.go
+++ b/stackframe.go
@@ -1,9 +1,9 @@
 package vm
 
-const FunctionMemoryEntries = 16
+const functionMemoryEntries = 16
 
-type StackFrame struct {
-	PreviousFunctionIndex    int64
-	PreviousInstructionIndex int64
-	FunctionMemory           [FunctionMemoryEntries]uint64
+type stackFrame struct {
+	previousFunctionIndex    int64
+	previousInstructionIndex int64
+	functionMemory           [functionMemoryEntries]uint64
 }
diff --git a/state.go b/state.go
index 9c024e2..89c0ae3 100644
--- a/state.go
+++ b/state.go
@@ -16,7 +16,7 @@ type State struct {
 
 	comparisonResult bool
 	globalMemory     [globalMemoryEntries]uint64
-	stack            []*StackFrame
+	stack            []*stackFrame
 }
 
 func NewState(functions [][]*Instruction) (*State, error) {
@@ -50,7 +50,7 @@ func (state *State) Execute() {
 	}
 }
 
-func (state *State) stackFrame() *StackFrame {
+func (state *State) stackFrame() *stackFrame {
 	return state.stack[len(state.stack)-1]
 }
 
@@ -90,11 +90,11 @@ func (state *State) readUnsigned(op *Operand) uint64 {
 		return op.Value
 
 	case FunctionMemoryIndex:
-		if op.Value >= FunctionMemoryEntries {
+		if op.Value >= functionMemoryEntries {
 			state.setError(fmt.Errorf("Invalid function memory index: %016x", op.Value))
 			return 0
 		}
-		return state.stackFrame().FunctionMemory[op.Value]
+		return state.stackFrame().functionMemory[op.Value]
 
 	case GlobalMemoryIndex:
 		if op.Value >= globalMemoryEntries {
@@ -119,11 +119,11 @@ func (state *State) writeUnsigned(op *Operand, value uint64) {
 		state.setError(fmt.Errorf("Write to literal operand"))
 
 	case FunctionMemoryIndex:
-		if op.Value >= FunctionMemoryEntries {
+		if op.Value >= functionMemoryEntries {
 			state.setError(fmt.Errorf("Invalid function memory index: %016x", op.Value))
 			return
 		}
-		state.stackFrame().FunctionMemory[op.Value] = value
+		state.stackFrame().functionMemory[op.Value] = value
 
 	case GlobalMemoryIndex:
 		if op.Value >= globalMemoryEntries {
@@ -147,9 +147,9 @@ func (state *State) call(functionOffset int64) {
 		return
 	}
 
-	stackFrame := &StackFrame{
-		PreviousFunctionIndex:    state.functionIndex,
-		PreviousInstructionIndex: state.instructionIndex,
+	stackFrame := &stackFrame{
+		previousFunctionIndex:    state.functionIndex,
+		previousInstructionIndex: state.instructionIndex,
 	}
 	state.stack = append(state.stack, stackFrame)
 	state.functionIndex += functionOffset
@@ -157,8 +157,8 @@ func (state *State) call(functionOffset int64) {
 }
 
 func (state *State) ret() {
-	state.functionIndex = state.stackFrame().PreviousFunctionIndex
-	state.instructionIndex = state.stackFrame().PreviousInstructionIndex
+	state.functionIndex = state.stackFrame().previousFunctionIndex
+	state.instructionIndex = state.stackFrame().previousInstructionIndex
 	state.stack = state.stack[:len(state.stack)-1]
 	if len(state.stack) == 0 {
 		state.running = false