diff --git a/build/fietsje/deps_monogon.go b/build/fietsje/deps_monogon.go
index 54e7d94..0abcd66 100644
--- a/build/fietsje/deps_monogon.go
+++ b/build/fietsje/deps_monogon.go
@@ -7,7 +7,7 @@
 import (
 	"bytes"
 	"fmt"
-	"io/ioutil"
+	"os"
 )
 
 // Monogon runs fietsje for all Monogon transitive dependencies.
@@ -134,7 +134,7 @@
 		return fmt.Errorf("could not render deps: %w", err)
 	}
 
-	err = ioutil.WriteFile(repositoriesBzlPath, buf.Bytes(), 0666)
+	err = os.WriteFile(repositoriesBzlPath, buf.Bytes(), 0666)
 	if err != nil {
 		return fmt.Errorf("could not write deps: %w", err)
 	}
diff --git a/build/fietsje/shelf.go b/build/fietsje/shelf.go
index 807ee44..c377186 100644
--- a/build/fietsje/shelf.go
+++ b/build/fietsje/shelf.go
@@ -19,7 +19,6 @@
 import (
 	"bytes"
 	"fmt"
-	"io/ioutil"
 	"log"
 	"os"
 	"sort"
@@ -69,7 +68,7 @@
 	if _, err := os.Stat(path); os.IsNotExist(err) {
 		log.Printf("Creating new shelf file at %q, this run will be slow.", path)
 	} else {
-		data, err = ioutil.ReadFile(path)
+		data, err = os.ReadFile(path)
 		if err != nil {
 			return nil, fmt.Errorf("could not read shelf: %v", err)
 		}
@@ -154,7 +153,7 @@
 	}
 
 	// And write it out.
-	err = ioutil.WriteFile(s.path, buf.Bytes(), 0644)
+	err = os.WriteFile(s.path, buf.Bytes(), 0644)
 	if err != nil {
 		return fmt.Errorf("could not write shelf: %v", err)
 	}
diff --git a/build/fietsje/transitive.go b/build/fietsje/transitive.go
index 2e2a9f7..6ffd594 100644
--- a/build/fietsje/transitive.go
+++ b/build/fietsje/transitive.go
@@ -18,7 +18,6 @@
 
 import (
 	"fmt"
-	"io/ioutil"
 	"log"
 	"os"
 	"strings"
@@ -61,7 +60,7 @@
 
 	read := func(p string) []byte {
 		full := fmt.Sprintf("%s/%s", path, p)
-		data, err := ioutil.ReadFile(full)
+		data, err := os.ReadFile(full)
 		if err != nil {
 			panic(fmt.Sprintf("reading file %q: %v", full, err))
 		}