diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 54af176..1f3b02d 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -30,8 +30,8 @@ jobs:
       shell: bash
     - name: Vet
       run: go vet ./...
-    #- name: Staticcheck
-    # if: matrix.go-version != '1.16.x'
-    #  run: staticcheck ./...
+    - name: Staticcheck
+      if: matrix.go-version != '1.16.x'
+      run: staticcheck ./...
     - name: Test
       run: go test -race ./...
\ No newline at end of file
diff --git a/afero.go b/afero.go
index 469ff7d..199480c 100644
--- a/afero.go
+++ b/afero.go
@@ -103,8 +103,8 @@ type Fs interface {
 
 var (
 	ErrFileClosed        = errors.New("File is closed")
-	ErrOutOfRange        = errors.New("Out of range")
-	ErrTooLarge          = errors.New("Too large")
+	ErrOutOfRange        = errors.New("out of range")
+	ErrTooLarge          = errors.New("too large")
 	ErrFileNotFound      = os.ErrNotExist
 	ErrFileExists        = os.ErrExist
 	ErrDestinationExists = os.ErrExist
diff --git a/afero_test.go b/afero_test.go
index e2c1362..5cd0a1a 100644
--- a/afero_test.go
+++ b/afero_test.go
@@ -98,7 +98,7 @@ func TestOpenFile(t *testing.T) {
 		io.WriteString(f, "|append")
 		f.Close()
 
-		f, err = fs.OpenFile(path, os.O_RDONLY, 0600)
+		f, _ = fs.OpenFile(path, os.O_RDONLY, 0600)
 		contents, _ := ioutil.ReadAll(f)
 		expectedContents := "initial|append"
 		if string(contents) != expectedContents {
@@ -700,7 +700,7 @@ func removeAllTestFiles(t *testing.T) {
 func equal(name1, name2 string) (r bool) {
 	switch runtime.GOOS {
 	case "windows":
-		r = strings.ToLower(name1) == strings.ToLower(name2)
+		r = strings.EqualFold(name1, name2)
 	default:
 		r = name1 == name2
 	}
diff --git a/composite_test.go b/composite_test.go
index 9cfbed9..05605fb 100644
--- a/composite_test.go
+++ b/composite_test.go
@@ -79,7 +79,7 @@ func TestUnionCreateExisting(t *testing.T) {
 	fh.Close()
 
 	fh, _ = base.Open("/home/test/file.txt")
-	data, err = ioutil.ReadAll(fh)
+	data, _ = ioutil.ReadAll(fh)
 	if string(data) != "This is a test" {
 		t.Errorf("Got wrong data in base file")
 	}
@@ -326,9 +326,9 @@ func TestUnionCacheWrite(t *testing.T) {
 		t.Errorf("Failed to write file")
 	}
 
-	fh.Seek(0, os.SEEK_SET)
+	fh.Seek(0, io.SeekStart)
 	buf := make([]byte, 4)
-	_, err = fh.Read(buf)
+	_, _ = fh.Read(buf)
 	fh.Write([]byte(" IS A"))
 	fh.Close()
 
diff --git a/gcsfs/fs.go b/gcsfs/fs.go
index 51db995..9b0dde4 100644
--- a/gcsfs/fs.go
+++ b/gcsfs/fs.go
@@ -302,6 +302,9 @@ func (fs *Fs) Remove(name string) error {
 		}
 		var infos []os.FileInfo
 		infos, err = dir.Readdir(0)
+		if err != nil {
+			return err
+		}
 		if len(infos) > 0 {
 			return syscall.ENOTEMPTY
 		}
@@ -345,6 +348,9 @@ func (fs *Fs) RemoveAll(path string) error {
 
 	var infos []os.FileInfo
 	infos, err = dir.Readdir(0)
+	if err != nil {
+		return err
+	}
 	for _, info := range infos {
 		nameToRemove := fs.normSeparators(info.Name())
 		err = fs.RemoveAll(path + fs.separator + nameToRemove)
diff --git a/gcsfs/gcs_test.go b/gcsfs/gcs_test.go
index 0809c2b..feedfb0 100644
--- a/gcsfs/gcs_test.go
+++ b/gcsfs/gcs_test.go
@@ -496,7 +496,7 @@ func TestGcsOpenFile(t *testing.T) {
 				t.Fatalf("failed to close a file \"%s\": %s", name, err)
 			}
 
-			file, err = gcsAfs.OpenFile(name, os.O_CREATE, 0600)
+			_, err = gcsAfs.OpenFile(name, os.O_CREATE, 0600)
 			if !errors.Is(err, syscall.EPERM) {
 				t.Errorf("%v: open for write: got %v, expected %v", name, err, syscall.EPERM)
 			}
diff --git a/httpFs.go b/httpFs.go
index 2b86e30..ac0de6d 100644
--- a/httpFs.go
+++ b/httpFs.go
@@ -29,7 +29,7 @@ type httpDir struct {
 }
 
 func (d httpDir) Open(name string) (http.File, error) {
-	if filepath.Separator != '/' && strings.IndexRune(name, filepath.Separator) >= 0 ||
+	if filepath.Separator != '/' && strings.ContainsRune(name, filepath.Separator) ||
 		strings.Contains(name, "\x00") {
 		return nil, errors.New("http: invalid character in file path")
 	}
diff --git a/ioutil_test.go b/ioutil_test.go
index 892705b..540bf56 100644
--- a/ioutil_test.go
+++ b/ioutil_test.go
@@ -37,13 +37,13 @@ func TestReadFile(t *testing.T) {
 
 	testFS.Create("this_exists.go")
 	filename := "rumpelstilzchen"
-	contents, err := fsutil.ReadFile(filename)
+	_, err := fsutil.ReadFile(filename)
 	if err == nil {
 		t.Fatalf("ReadFile %s: error expected, none found", filename)
 	}
 
 	filename = "this_exists.go"
-	contents, err = fsutil.ReadFile(filename)
+	contents, err := fsutil.ReadFile(filename)
 	if err != nil {
 		t.Fatalf("ReadFile %s: %v", filename, err)
 	}
diff --git a/mem/file.go b/mem/file.go
index 5ef8b6a..258880b 100644
--- a/mem/file.go
+++ b/mem/file.go
@@ -186,7 +186,7 @@ func (f *File) Readdirnames(n int) (names []string, err error) {
 func (f *File) Read(b []byte) (n int, err error) {
 	f.fileData.Lock()
 	defer f.fileData.Unlock()
-	if f.closed == true {
+	if f.closed {
 		return 0, ErrFileClosed
 	}
 	if len(b) > 0 && int(f.at) == len(f.fileData.data) {
@@ -214,7 +214,7 @@ func (f *File) ReadAt(b []byte, off int64) (n int, err error) {
 }
 
 func (f *File) Truncate(size int64) error {
-	if f.closed == true {
+	if f.closed {
 		return ErrFileClosed
 	}
 	if f.readOnly {
@@ -236,7 +236,7 @@ func (f *File) Truncate(size int64) error {
 }
 
 func (f *File) Seek(offset int64, whence int) (int64, error) {
-	if f.closed == true {
+	if f.closed {
 		return 0, ErrFileClosed
 	}
 	switch whence {
@@ -251,7 +251,7 @@ func (f *File) Seek(offset int64, whence int) (int64, error) {
 }
 
 func (f *File) Write(b []byte) (n int, err error) {
-	if f.closed == true {
+	if f.closed {
 		return 0, ErrFileClosed
 	}
 	if f.readOnly {
@@ -330,8 +330,8 @@ func (s *FileInfo) Size() int64 {
 
 var (
 	ErrFileClosed        = errors.New("File is closed")
-	ErrOutOfRange        = errors.New("Out of range")
-	ErrTooLarge          = errors.New("Too large")
+	ErrOutOfRange        = errors.New("out of range")
+	ErrTooLarge          = errors.New("too large")
 	ErrFileNotFound      = os.ErrNotExist
 	ErrFileExists        = os.ErrExist
 	ErrDestinationExists = os.ErrExist
diff --git a/memmap_test.go b/memmap_test.go
index 881a61b..94f70b2 100644
--- a/memmap_test.go
+++ b/memmap_test.go
@@ -214,7 +214,7 @@ func TestMultipleOpenFiles(t *testing.T) {
 		if err != nil {
 			t.Error("fh.Write failed: " + err.Error())
 		}
-		_, err = fh1.Seek(0, os.SEEK_SET)
+		_, err = fh1.Seek(0, io.SeekStart)
 		if err != nil {
 			t.Error(err)
 		}
diff --git a/ro_regexp_test.go b/ro_regexp_test.go
index ef8a35d..ef3a14f 100644
--- a/ro_regexp_test.go
+++ b/ro_regexp_test.go
@@ -16,12 +16,12 @@ func TestFilterReadOnly(t *testing.T) {
 
 func TestFilterReadonlyRemoveAndRead(t *testing.T) {
 	mfs := &MemMapFs{}
-	fh, err := mfs.Create("/file.txt")
+	fh, _ := mfs.Create("/file.txt")
 	fh.Write([]byte("content here"))
 	fh.Close()
 
 	fs := NewReadOnlyFs(mfs)
-	err = fs.Remove("/file.txt")
+	err := fs.Remove("/file.txt")
 	if err == nil {
 		t.Errorf("Did not fail to remove file")
 	}
diff --git a/sftpfs/sftp_test.go b/sftpfs/sftp_test.go
index 4dba7fc..a865139 100644
--- a/sftpfs/sftp_test.go
+++ b/sftpfs/sftp_test.go
@@ -215,6 +215,9 @@ func MakeSSHKeyPair(bits int, pubKeyPath, privateKeyPath string) error {
 
 	// generate and write private key as PEM
 	privateKeyFile, err := os.Create(privateKeyPath)
+	if err != nil {
+		return err
+	}
 	defer privateKeyFile.Close()
 	if err != nil {
 		return err
diff --git a/tarfs/tarfs_test.go b/tarfs/tarfs_test.go
index c588c79..aa2d6a4 100644
--- a/tarfs/tarfs_test.go
+++ b/tarfs/tarfs_test.go
@@ -266,7 +266,7 @@ func TestOpenFile(t *testing.T) {
 		}
 		file.Close()
 
-		file, err = afs.OpenFile(f.name, os.O_CREATE, 0600)
+		_, err = afs.OpenFile(f.name, os.O_CREATE, 0600)
 		if !errors.Is(err, syscall.EPERM) {
 			t.Errorf("%v: open for write: got %v, expected %v", f.name, err, syscall.EPERM)
 		}
diff --git a/unionFile.go b/unionFile.go
index 34f99a4..333d367 100644
--- a/unionFile.go
+++ b/unionFile.go
@@ -65,7 +65,7 @@ func (f *UnionFile) ReadAt(s []byte, o int64) (int, error) {
 	if f.Layer != nil {
 		n, err := f.Layer.ReadAt(s, o)
 		if (err == nil || err == io.EOF) && f.Base != nil {
-			_, err = f.Base.Seek(o+int64(n), os.SEEK_SET)
+			_, err = f.Base.Seek(o+int64(n), io.SeekStart)
 		}
 		return n, err
 	}
diff --git a/util.go b/util.go
index 4f253f4..cb7de23 100644
--- a/util.go
+++ b/util.go
@@ -25,6 +25,7 @@ import (
 	"strings"
 	"unicode"
 
+	"golang.org/x/text/runes"
 	"golang.org/x/text/transform"
 	"golang.org/x/text/unicode/norm"
 )
@@ -158,16 +159,12 @@ func UnicodeSanitize(s string) string {
 
 // Transform characters with accents into plain forms.
 func NeuterAccents(s string) string {
-	t := transform.Chain(norm.NFD, transform.RemoveFunc(isMn), norm.NFC)
+	t := transform.Chain(norm.NFD, runes.Remove(runes.In(unicode.Mn)), norm.NFC)
 	result, _, _ := transform.String(t, string(s))
 
 	return result
 }
 
-func isMn(r rune) bool {
-	return unicode.Is(unicode.Mn, r) // Mn: nonspacing marks
-}
-
 func (a Afero) FileContainsBytes(filename string, subslice []byte) (bool, error) {
 	return FileContainsBytes(a.Fs, filename, subslice)
 }
@@ -299,6 +296,9 @@ func IsEmpty(fs Fs, path string) (bool, error) {
 		}
 		defer f.Close()
 		list, err := f.Readdir(-1)
+		if err != nil {
+			return false, err
+		}
 		return len(list) == 0, nil
 	}
 	return fi.Size() == 0, nil
diff --git a/util_test.go b/util_test.go
index d2145cf..985b7a1 100644
--- a/util_test.go
+++ b/util_test.go
@@ -185,7 +185,7 @@ func createZeroSizedFileInTempDir() (File, error) {
 func createNonZeroSizedFileInTempDir() (File, error) {
 	f, err := createZeroSizedFileInTempDir()
 	if err != nil {
-		// no file ??
+		return nil, err
 	}
 	byteString := []byte("byteString")
 	err = WriteFile(testFS, f.Name(), byteString, 0644)
@@ -200,7 +200,7 @@ func createNonZeroSizedFileInTempDir() (File, error) {
 func deleteFileInTempDir(f File) {
 	err := testFS.Remove(f.Name())
 	if err != nil {
-		// now what?
+		panic(err)
 	}
 }
 
@@ -217,7 +217,7 @@ func createEmptyTempDir() (string, error) {
 func createTempDirWithZeroLengthFiles() (string, error) {
 	d, dirErr := createEmptyTempDir()
 	if dirErr != nil {
-		//now what?
+		return "", dirErr
 	}
 	filePrefix := "_path_test_"
 	_, fileErr := TempFile(testFS, d, filePrefix) // dir is os.TempDir()
@@ -235,7 +235,7 @@ func createTempDirWithZeroLengthFiles() (string, error) {
 func createTempDirWithNonZeroLengthFiles() (string, error) {
 	d, dirErr := createEmptyTempDir()
 	if dirErr != nil {
-		//now what?
+		return "", dirErr
 	}
 	filePrefix := "_path_test_"
 	f, fileErr := TempFile(testFS, d, filePrefix) // dir is os.TempDir()
@@ -406,7 +406,7 @@ func TestGetTempDir(t *testing.T) {
 func deleteTempDir(d string) {
 	err := os.RemoveAll(d)
 	if err != nil {
-		// now what?
+		panic(err)
 	}
 }
 
diff --git a/zipfs/file.go b/zipfs/file.go
index 355f5f4..9b7ddbe 100644
--- a/zipfs/file.go
+++ b/zipfs/file.go
@@ -85,10 +85,10 @@ func (f *File) Seek(offset int64, whence int) (int64, error) {
 		return 0, afero.ErrFileClosed
 	}
 	switch whence {
-	case os.SEEK_SET:
-	case os.SEEK_CUR:
+	case io.SeekStart:
+	case io.SeekCurrent:
 		offset += f.offset
-	case os.SEEK_END:
+	case io.SeekEnd:
 		offset += int64(f.zipfile.UncompressedSize64)
 	default:
 		return 0, syscall.EINVAL