diff --git a/linter/file.go b/linter/file.go
index 28b0602..0fddaa9 100644
--- a/linter/file.go
+++ b/linter/file.go
@@ -13,19 +13,19 @@ import (
 type File struct {
 	Name    string
 	pkg     *Package
-	Content []byte
+	content []byte
 	ast     *ast.File
 }
 
 // NewFile creates a new file
 func NewFile(name string, content []byte, pkg *Package) (*File, error) {
-	f, err := parser.ParseFile(pkg.Fset, name, content, parser.ParseComments)
+	f, err := parser.ParseFile(pkg.fset, name, content, parser.ParseComments)
 	if err != nil {
 		return nil, err
 	}
 	return &File{
 		Name:    name,
-		Content: content,
+		content: content,
 		pkg:     pkg,
 		ast:     f,
 	}, nil
@@ -33,7 +33,7 @@ func NewFile(name string, content []byte, pkg *Package) (*File, error) {
 
 // ToPosition returns line and column for given position.
 func (f *File) ToPosition(pos token.Pos) token.Position {
-	return f.pkg.Fset.Position(pos)
+	return f.pkg.fset.Position(pos)
 }
 
 // GetAST returns the AST of the file
diff --git a/linter/linter.go b/linter/linter.go
index 0eea47f..82082a8 100644
--- a/linter/linter.go
+++ b/linter/linter.go
@@ -44,8 +44,8 @@ func isGenerated(src []byte) bool {
 // Lint lints a set of files with the specified rule.
 func (l *Linter) Lint(filenames []string, ruleSet []Rule, rulesConfig RulesConfig) ([]Failure, error) {
 	pkg := &Package{
-		Fset:  token.NewFileSet(),
-		Files: map[string]*File{},
+		fset:  token.NewFileSet(),
+		files: map[string]*File{},
 	}
 	var pkgName string
 	for _, filename := range filenames {
@@ -68,7 +68,7 @@ func (l *Linter) Lint(filenames []string, ruleSet []Rule, rulesConfig RulesConfi
 			return nil, fmt.Errorf("%s is in package %s, not %s", filename, file.GetAST().Name.Name, pkgName)
 		}
 
-		pkg.Files[filename] = file
+		pkg.files[filename] = file
 	}
 
 	return pkg.lint(ruleSet, rulesConfig), nil
diff --git a/linter/package.go b/linter/package.go
index 296796c..946ea57 100644
--- a/linter/package.go
+++ b/linter/package.go
@@ -10,8 +10,8 @@ import (
 
 // Package represents a package in the project.
 type Package struct {
-	Fset  *token.FileSet
-	Files map[string]*File
+	fset  *token.FileSet
+	files map[string]*File
 
 	TypesPkg  *types.Package
 	TypesInfo *types.Info
@@ -39,7 +39,7 @@ func (p *Package) IsMain() bool {
 	} else if p.main == falseValue {
 		return false
 	}
-	for _, f := range p.Files {
+	for _, f := range p.files {
 		if f.isMain() {
 			p.main = trueValue
 			return true
@@ -54,7 +54,7 @@ func (p *Package) TypeCheck() error {
 	config := &types.Config{
 		// By setting a no-op error reporter, the type checker does as much work as possible.
 		Error:    func(error) {},
-		Importer: newImporter(p.Fset),
+		Importer: newImporter(p.fset),
 	}
 	info := &types.Info{
 		Types:  make(map[ast.Expr]types.TypeAndValue),
@@ -64,11 +64,11 @@ func (p *Package) TypeCheck() error {
 	}
 	var anyFile *File
 	var astFiles []*ast.File
-	for _, f := range p.Files {
+	for _, f := range p.files {
 		anyFile = f
 		astFiles = append(astFiles, f.GetAST())
 	}
-	typesPkg, err := config.Check(anyFile.GetAST().Name.Name, p.Fset, astFiles, info)
+	typesPkg, err := config.Check(anyFile.GetAST().Name.Name, p.fset, astFiles, info)
 	// Remember the typechecking info, even if config.Check failed,
 	// since we will get partial information.
 	p.TypesPkg = typesPkg
@@ -79,7 +79,7 @@ func (p *Package) TypeCheck() error {
 func (p *Package) lint(rules []Rule, config RulesConfig) []Failure {
 	var failures []Failure
 	p.TypeCheck()
-	for _, file := range p.Files {
+	for _, file := range p.files {
 		failures = append(failures, file.lint(rules, config)...)
 	}
 	return failures