diff --git a/file_handling.go b/file_handling.go
index 7c0b1a7..a3538b4 100644
--- a/file_handling.go
+++ b/file_handling.go
@@ -7,8 +7,8 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
-
-	"golang.org/x/tools/godoc/util"
+	"unicode/utf8"
+	"bytes"
 )
 
 type File struct {
@@ -60,8 +60,8 @@ func (f *File) Mode() (os.FileMode, error) {
 }
 
 // Read reads the file into a string, or returns the empty string for binary
-// files. An error indicates the file could not be opened or fully read; the
-// caller should log-and-skip rather than abort.
+// files (NUL bytes or invalid UTF-8). An error indicates the file could not be
+// opened or fully read; the caller should log-and-skip rather than abort.
 func (f *File) Read() (string, error) {
 	handle, err := os.Open(f.Path)
 	if err != nil {
@@ -69,21 +69,46 @@ func (f *File) Read() (string, error) {
 	}
 	defer handle.Close()
 
-	// Check if the file looks like text before reading the entire file.
 	var buf [1024]byte
-	n, err := handle.Read(buf[0:])
-	if err != nil || !util.IsText(buf[0:n]) {
+	n, err := handle.Read(buf[:])
+	if err != nil && err != io.EOF {
+		return "", fmt.Errorf("read %v: %w", f.Path, err)
+	}
+	if n == 0 {
 		return "", nil
 	}
-
-	// Reset file handle so we can read the entire file.
-	if _, err := handle.Seek(0, io.SeekStart); err != nil {
-		return "", fmt.Errorf("seek to start of %v: %w", f.Path, err)
+	if !isTextBytes(buf[:n]) {
+		return "", nil
+	}
+	if err == io.EOF {
+		return string(buf[:n]), nil
 	}
 
 	builder := new(strings.Builder)
-	if _, err := io.Copy(builder, handle); err != nil {
-		return "", fmt.Errorf("read %v: %w", f.Path, err)
+	if _, wErr := builder.Write(buf[:n]); wErr != nil {
+		return "", fmt.Errorf("read %v: %w", f.Path, wErr)
+	}
+
+	chunk := make([]byte, 32*1024)
+	for {
+		readN, readErr := handle.Read(chunk)
+		if readN > 0 {
+			if bytes.IndexByte(chunk[:readN], 0) >= 0 {
+				return "", nil
+			}
+			if !utf8.Valid(chunk[:readN]) {
+				return "", nil
+			}
+			if _, wErr := builder.Write(chunk[:readN]); wErr != nil {
+				return "", fmt.Errorf("read %v: %w", f.Path, wErr)
+			}
+		}
+		if readErr == io.EOF {
+			break
+		}
+		if readErr != nil {
+			return "", fmt.Errorf("read %v: %w", f.Path, readErr)
+		}
 	}
 	return builder.String(), nil
 }
diff --git a/file_handling_test.go b/file_handling_test.go
index 91ee538..17f2e26 100644
--- a/file_handling_test.go
+++ b/file_handling_test.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+	"os"
 	"path/filepath"
 	"testing"
 )
@@ -77,3 +78,44 @@ func TestNewFile(t *testing.T) {
 		})
 	}
 }
+
+func TestReadSkipsBinaryWithNUL(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "mixed.txt")
+	content := []byte("text prefix\x00binary suffix")
+	if err := os.WriteFile(path, content, 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	f, err := NewFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	got, err := f.Read()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got != "" {
+		t.Fatalf("Read() = %q; want empty for NUL-containing file", got)
+	}
+}
+
+func TestReadReturnsShortTextFile(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "short.txt")
+	if err := os.WriteFile(path, []byte("hello"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	f, err := NewFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	got, err := f.Read()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got != "hello" {
+		t.Fatalf("Read() = %q; want %q", got, "hello")
+	}
+}
+
diff --git a/go.mod b/go.mod
index 66fd9af..d0c7f3d 100644
--- a/go.mod
+++ b/go.mod
@@ -1,5 +1,3 @@
 module github.com/dolph/find-replace
 
 go 1.20
-
-require golang.org/x/tools v0.7.0
diff --git a/go.sum b/go.sum
index b522ba0..e69de29 100644
--- a/go.sum
+++ b/go.sum
@@ -1,4 +0,0 @@
-golang.org/x/tools v0.1.9 h1:j9KsMiaP1c3B0OTQGth0/k+miLGTgLsAFUCrF2vLcF8=
-golang.org/x/tools v0.1.9/go.mod h1:nABZi5QlRsZVlzPpHl034qft6wpY4eDcsTt5AaioBiU=
-golang.org/x/tools v0.7.0 h1:W4OVu8VVOaIO0yzWMNdepAulS7YfoS3Zabrm8DOXXU4=
-golang.org/x/tools v0.7.0/go.mod h1:4pg6aUX35JBAogB10C9AtvVL+qowtN4pT3CGSQex14s=
diff --git a/text_detect.go b/text_detect.go
new file mode 100644
index 0000000..ae50590
--- /dev/null
+++ b/text_detect.go
@@ -0,0 +1,17 @@
+package main
+
+import (
+	"bytes"
+	"unicode/utf8"
+)
+
+// isTextBytes reports whether b is valid UTF-8 and contains no NUL bytes.
+func isTextBytes(b []byte) bool {
+	if len(b) == 0 {
+		return true
+	}
+	if bytes.IndexByte(b, 0) >= 0 {
+		return false
+	}
+	return utf8.Valid(b)
+}
diff --git a/text_detect_test.go b/text_detect_test.go
new file mode 100644
index 0000000..05810a9
--- /dev/null
+++ b/text_detect_test.go
@@ -0,0 +1,24 @@
+package main
+
+import "testing"
+
+func TestIsTextBytes(t *testing.T) {
+	cases := []struct {
+		name string
+		in   []byte
+		want bool
+	}{
+		{name: "empty", in: nil, want: true},
+		{name: "ascii", in: []byte("hello"), want: true},
+		{name: "utf8", in: []byte("héllo"), want: true},
+		{name: "nul", in: []byte("a\x00b"), want: false},
+		{name: "invalid utf8", in: []byte{0xff, 0xfe}, want: false},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := isTextBytes(tc.in); got != tc.want {
+				t.Fatalf("isTextBytes(%q) = %v; want %v", tc.in, got, tc.want)
+			}
+		})
+	}
+}