diff --git a/builder/builder_test.go b/builder/builder_test.go
index 42727e4a..3b0ae8bc 100644
--- a/builder/builder_test.go
+++ b/builder/builder_test.go
@@ -2,7 +2,6 @@ package builder
 
 import (
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -90,7 +89,7 @@ func testClangAttributes(t *testing.T, options *compileopts.Options) {
 
 	// Create a very simple C input file.
 	srcpath := filepath.Join(testDir, "test.c")
-	err = ioutil.WriteFile(srcpath, []byte("int add(int a, int b) { return a + b; }"), 0o666)
+	err = os.WriteFile(srcpath, []byte("int add(int a, int b) { return a + b; }"), 0o666)
 	if err != nil {
 		t.Fatalf("could not write target file %s: %s", srcpath, err)
 	}
diff --git a/cgo/cgo_test.go b/cgo/cgo_test.go
index cbb0f589..c542df7f 100644
--- a/cgo/cgo_test.go
+++ b/cgo/cgo_test.go
@@ -10,7 +10,7 @@ import (
 	"go/parser"
 	"go/token"
 	"go/types"
-	"io/ioutil"
+	"os"
 	"path/filepath"
 	"runtime"
 	"strings"
@@ -107,7 +107,7 @@ func TestCGo(t *testing.T) {
 
 			// Read the file with the expected output, to compare against.
 			outfile := filepath.Join("testdata", name+".out.go")
-			expectedBytes, err := ioutil.ReadFile(outfile)
+			expectedBytes, err := os.ReadFile(outfile)
 			if err != nil {
 				t.Fatalf("could not read expected output: %v", err)
 			}
@@ -118,7 +118,7 @@ func TestCGo(t *testing.T) {
 				// It is not. Test failed.
 				if *flagUpdate {
 					// Update the file with the expected data.
-					err := ioutil.WriteFile(outfile, []byte(actual), 0666)
+					err := os.WriteFile(outfile, []byte(actual), 0666)
 					if err != nil {
 						t.Error("could not write updated output file:", err)
 					}
diff --git a/compiler/compiler_test.go b/compiler/compiler_test.go
index cee023cd..e115cf95 100644
--- a/compiler/compiler_test.go
+++ b/compiler/compiler_test.go
@@ -3,7 +3,7 @@ package compiler
 import (
 	"flag"
 	"go/types"
-	"io/ioutil"
+	"os"
 	"strconv"
 	"strings"
 	"testing"
@@ -162,14 +162,14 @@ func TestCompiler(t *testing.T) {
 
 			// Update test if needed. Do not check the result.
 			if *flagUpdate {
-				err := ioutil.WriteFile(outPath, []byte(mod.String()), 0666)
+				err := os.WriteFile(outPath, []byte(mod.String()), 0666)
 				if err != nil {
 					t.Error("failed to write updated output file:", err)
 				}
 				return
 			}
 
-			expected, err := ioutil.ReadFile(outPath)
+			expected, err := os.ReadFile(outPath)
 			if err != nil {
 				t.Fatal("failed to read golden file:", err)
 			}
diff --git a/interp/interp_test.go b/interp/interp_test.go
index 7b2bb619..c4258653 100644
--- a/interp/interp_test.go
+++ b/interp/interp_test.go
@@ -1,7 +1,6 @@
 package interp
 
 import (
-	"io/ioutil"
 	"os"
 	"strconv"
 	"strings"
@@ -87,7 +86,7 @@ func runTest(t *testing.T, pathPrefix string) {
 	pm.Run(mod)
 
 	// Read the expected output IR.
-	out, err := ioutil.ReadFile(pathPrefix + ".out.ll")
+	out, err := os.ReadFile(pathPrefix + ".out.ll")
 	if err != nil {
 		t.Fatalf("could not read output file %s: %v", pathPrefix+".out.ll", err)
 	}
diff --git a/main_test.go b/main_test.go
index f620c77d..310a92fe 100644
--- a/main_test.go
+++ b/main_test.go
@@ -10,7 +10,6 @@ import (
 	"flag"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"os"
 	"os/exec"
 	"reflect"
@@ -319,7 +318,7 @@ func runTestWithConfig(name string, t *testing.T, options compileopts.Options, c
 	if path[len(path)-1] == '/' {
 		txtpath = path + "out.txt"
 	}
-	expected, err := ioutil.ReadFile(txtpath)
+	expected, err := os.ReadFile(txtpath)
 	if err != nil {
 		t.Fatal("could not read expected output file:", err)
 	}
diff --git a/src/os/os_anyos_test.go b/src/os/os_anyos_test.go
index d8ac01c2..dd255fb4 100644
--- a/src/os/os_anyos_test.go
+++ b/src/os/os_anyos_test.go
@@ -5,7 +5,7 @@ package os_test
 
 import (
 	"io/fs"
-	"io/ioutil"
+	"os"
 	. "os"
 	"path/filepath"
 	"runtime"
@@ -198,13 +198,13 @@ func TestRenameOverwriteDest(t *testing.T) {
 	toData := []byte("to")
 	fromData := []byte("from")
 
-	err := ioutil.WriteFile(to, toData, 0777)
+	err := os.WriteFile(to, toData, 0777)
 	defer Remove(to) // TODO: switch to t.Tempdir, remove this line
 	if err != nil {
 		t.Fatalf("write file %q failed: %v", to, err)
 	}
 
-	err = ioutil.WriteFile(from, fromData, 0777)
+	err = os.WriteFile(from, fromData, 0777)
 	defer Remove(from) // TODO: switch to t.Tempdir, remove this line
 	if err != nil {
 		t.Fatalf("write file %q failed: %v", from, err)
diff --git a/src/os/os_test.go b/src/os/os_test.go
index bf1a1735..d79ad4a3 100644
--- a/src/os/os_test.go
+++ b/src/os/os_test.go
@@ -6,7 +6,7 @@ package os_test
 
 import (
 	"io"
-	"io/ioutil"
+	"os"
 	. "os"
 	"runtime"
 	"strings"
@@ -129,7 +129,7 @@ func TestSeek(t *testing.T) {
 		off, err := f.Seek(tt.in, tt.whence)
 		if off != tt.out || err != nil {
 			if e, ok := err.(*PathError); ok && e.Err == syscall.EINVAL && tt.out > 1<<32 && runtime.GOOS == "linux" {
-				mounts, _ := ioutil.ReadFile("/proc/mounts")
+				mounts, _ := os.ReadFile("/proc/mounts")
 				if strings.Contains(string(mounts), "reiserfs") {
 					// Reiserfs rejects the big seeks.
 					t.Skipf("skipping test known to fail on reiserfs; https://golang.org/issue/91")
diff --git a/transform/allocs_test.go b/transform/allocs_test.go
index f4c86f66..27bb9706 100644
--- a/transform/allocs_test.go
+++ b/transform/allocs_test.go
@@ -2,7 +2,7 @@ package transform_test
 
 import (
 	"go/token"
-	"io/ioutil"
+	"os"
 	"path/filepath"
 	"regexp"
 	"sort"
@@ -62,7 +62,7 @@ func TestAllocs2(t *testing.T) {
 	}
 
 	// Load expected test output (the OUT: lines).
-	testInput, err := ioutil.ReadFile("./testdata/allocs2.go")
+	testInput, err := os.ReadFile("./testdata/allocs2.go")
 	if err != nil {
 		t.Fatal("could not read test input:", err)
 	}
diff --git a/transform/transform_test.go b/transform/transform_test.go
index 1c6b5df3..4cab255e 100644
--- a/transform/transform_test.go
+++ b/transform/transform_test.go
@@ -6,7 +6,6 @@ import (
 	"flag"
 	"go/token"
 	"go/types"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -58,13 +57,13 @@ func testTransform(t *testing.T, pathPrefix string, transform func(mod llvm.Modu
 	actual = actual[strings.Index(actual, "\ntarget datalayout = ")+1:]
 
 	if *update {
-		err := ioutil.WriteFile(pathPrefix+".out.ll", []byte(actual), 0666)
+		err := os.WriteFile(pathPrefix+".out.ll", []byte(actual), 0666)
 		if err != nil {
 			t.Error("failed to write out new output:", err)
 		}
 	} else {
 		// Read the expected output IR.
-		out, err := ioutil.ReadFile(pathPrefix + ".out.ll")
+		out, err := os.ReadFile(pathPrefix + ".out.ll")
 		if err != nil {
 			t.Fatalf("could not read output file %s: %v", pathPrefix+".out.ll", err)
 		}