diff --git a/autopilot/autopilot.go b/autopilot/autopilot.go
index c53e4ec4c..eb08c9456 100644
--- a/autopilot/autopilot.go
+++ b/autopilot/autopilot.go
@@ -632,7 +632,7 @@ func (ap *Autopilot) isStopped() bool {
 
 func (ap *Autopilot) configHandlerGET(jc jape.Context) {
 	autopilot, err := ap.bus.Autopilot(jc.Request.Context(), ap.id)
-	if err != nil && strings.Contains(err.Error(), api.ErrAutopilotNotFound.Error()) {
+	if utils.IsErr(err, api.ErrAutopilotNotFound) {
 		jc.Error(errors.New("autopilot is not configured yet"), http.StatusNotFound)
 		return
 	}
@@ -654,7 +654,7 @@ func (ap *Autopilot) configHandlerPUT(jc jape.Context) {
 	// fetch the autopilot and update its config
 	var contractSetChanged bool
 	autopilot, err := ap.bus.Autopilot(jc.Request.Context(), ap.id)
-	if err != nil && strings.Contains(err.Error(), api.ErrAutopilotNotFound.Error()) {
+	if utils.IsErr(err, api.ErrAutopilotNotFound) {
 		autopilot = api.Autopilot{ID: ap.id, Config: cfg}
 	} else {
 		if autopilot.Config.Contracts.Set != cfg.Contracts.Set {
diff --git a/autopilot/contractor.go b/autopilot/contractor.go
index d69f2a354..8dfc702f3 100644
--- a/autopilot/contractor.go
+++ b/autopilot/contractor.go
@@ -1004,7 +1004,7 @@ func (c *contractor) runRevisionBroadcast(ctx context.Context, w Worker, allCont
 		ctx, cancel := context.WithTimeout(ctx, timeoutBroadcastRevision)
 		err := w.RHPBroadcast(ctx, contract.ID)
 		cancel()
-		if err != nil && strings.Contains(err.Error(), "transaction has a file contract with an outdated revision number") {
+		if utils.IsErr(err, errors.New("transaction has a file contract with an outdated revision number")) {
 			continue // don't log - revision was already broadcasted
 		} else if err != nil {
 			c.logger.Warnw(fmt.Sprintf("failed to broadcast contract revision: %v", err),
diff --git a/cmd/renterd/main.go b/cmd/renterd/main.go
index 98e075d92..093747796 100644
--- a/cmd/renterd/main.go
+++ b/cmd/renterd/main.go
@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"flag"
 	"fmt"
 	"log"
@@ -24,6 +25,7 @@ import (
 	"go.sia.tech/renterd/bus"
 	"go.sia.tech/renterd/config"
 	"go.sia.tech/renterd/internal/node"
+	"go.sia.tech/renterd/internal/utils"
 	"go.sia.tech/renterd/s3"
 	"go.sia.tech/renterd/stores"
 	"go.sia.tech/renterd/worker"
@@ -224,7 +226,7 @@ func parseEnvVar(s string, v interface{}) {
 
 func listenTCP(logger *zap.Logger, addr string) (net.Listener, error) {
 	l, err := net.Listen("tcp", addr)
-	if err != nil && strings.Contains(err.Error(), "no such host") && strings.Contains(addr, "localhost") {
+	if utils.IsErr(err, errors.New("no such host")) && strings.Contains(addr, "localhost") {
 		// fall back to 127.0.0.1 if 'localhost' doesn't work
 		_, port, err := net.SplitHostPort(addr)
 		if err != nil {
diff --git a/s3/authentication.go b/s3/authentication.go
index 215da52b7..67017356b 100644
--- a/s3/authentication.go
+++ b/s3/authentication.go
@@ -5,11 +5,11 @@ import (
 	"fmt"
 	"io"
 	"net/http"
-	"strings"
 
 	"go.sia.tech/gofakes3"
 	"go.sia.tech/gofakes3/signature"
 	"go.sia.tech/renterd/api"
+	"go.sia.tech/renterd/internal/utils"
 )
 
 var (
@@ -89,7 +89,7 @@ func newAuthenticatedBackend(b *s3) *authenticatedBackend {
 
 func (b *authenticatedBackend) applyBucketPolicy(ctx context.Context, bucketName string, p *permissions) error {
 	bucket, err := b.backend.b.Bucket(ctx, bucketName)
-	if err != nil && strings.Contains(err.Error(), api.ErrBucketNotFound.Error()) {
+	if utils.IsErr(err, api.ErrBucketNotFound) {
 		return gofakes3.BucketNotFound(bucketName)
 	} else if err != nil {
 		return gofakes3.ErrorMessage(gofakes3.ErrInternal, err.Error())
diff --git a/s3/backend.go b/s3/backend.go
index 5261bd5f7..62f7a3e76 100644
--- a/s3/backend.go
+++ b/s3/backend.go
@@ -10,6 +10,7 @@ import (
 
 	"go.sia.tech/gofakes3"
 	"go.sia.tech/renterd/api"
+	"go.sia.tech/renterd/internal/utils"
 	"go.sia.tech/renterd/object"
 	"go.uber.org/zap"
 )
@@ -109,7 +110,7 @@ func (s *s3) ListBucket(ctx context.Context, bucketName string, prefix *gofakes3
 		}
 		var res api.ObjectsResponse
 		res, err = s.b.Object(ctx, bucketName, path, opts)
-		if err != nil && strings.Contains(err.Error(), api.ErrBucketNotFound.Error()) {
+		if utils.IsErr(err, api.ErrBucketNotFound) {
 			return nil, gofakes3.BucketNotFound(bucketName)
 		} else if err != nil {
 			return nil, gofakes3.ErrorMessage(gofakes3.ErrInternal, err.Error())
@@ -129,7 +130,7 @@ func (s *s3) ListBucket(ctx context.Context, bucketName string, prefix *gofakes3
 
 		var res api.ObjectsListResponse
 		res, err = s.b.ListObjects(ctx, bucketName, opts)
-		if err != nil && strings.Contains(err.Error(), api.ErrBucketNotFound.Error()) {
+		if utils.IsErr(err, api.ErrBucketNotFound) {
 			return nil, gofakes3.BucketNotFound(bucketName)
 		} else if err != nil {
 			return nil, gofakes3.ErrorMessage(gofakes3.ErrInternal, err.Error())
@@ -169,7 +170,7 @@ func (s *s3) ListBucket(ctx context.Context, bucketName string, prefix *gofakes3
 // gofakes3.ErrBucketAlreadyExists MUST be returned.
 func (s *s3) CreateBucket(ctx context.Context, name string) error {
 	err := s.b.CreateBucket(ctx, name, api.CreateBucketOptions{})
-	if err != nil && strings.Contains(err.Error(), api.ErrBucketExists.Error()) {
+	if utils.IsErr(err, api.ErrBucketExists) {
 		return gofakes3.ErrBucketAlreadyExists
 	} else if err != nil {
 		return gofakes3.ErrorMessage(gofakes3.ErrInternal, err.Error())
@@ -183,7 +184,7 @@ func (s *s3) CreateBucket(ctx context.Context, name string) error {
 // TODO: backend could be improved to allow for checking specific dir in root.
 func (s *s3) BucketExists(ctx context.Context, name string) (bool, error) {
 	_, err := s.b.Bucket(ctx, name)
-	if err != nil && strings.Contains(err.Error(), api.ErrBucketNotFound.Error()) {
+	if utils.IsErr(err, api.ErrBucketNotFound) {
 		return false, nil
 	} else if err != nil {
 		return false, gofakes3.ErrorMessage(gofakes3.ErrInternal, err.Error())
@@ -203,9 +204,9 @@ func (s *s3) BucketExists(ctx context.Context, name string) (bool, error) {
 // atomically checking whether a bucket is empty.
 func (s *s3) DeleteBucket(ctx context.Context, name string) error {
 	err := s.b.DeleteBucket(ctx, name)
-	if err != nil && strings.Contains(err.Error(), api.ErrBucketNotEmpty.Error()) {
+	if utils.IsErr(err, api.ErrBucketNotEmpty) {
 		return gofakes3.ErrBucketNotEmpty
-	} else if err != nil && strings.Contains(err.Error(), api.ErrBucketNotFound.Error()) {
+	} else if utils.IsErr(err, api.ErrBucketNotFound) {
 		return gofakes3.BucketNotFound(name)
 	} else if err != nil {
 		return gofakes3.ErrorMessage(gofakes3.ErrInternal, err.Error())
@@ -243,9 +244,9 @@ func (s *s3) GetObject(ctx context.Context, bucketName, objectName string, range
 	}
 
 	res, err := s.w.GetObject(ctx, bucketName, objectName, opts)
-	if err != nil && strings.Contains(err.Error(), api.ErrBucketNotFound.Error()) {
+	if utils.IsErr(err, api.ErrBucketNotFound) {
 		return nil, gofakes3.BucketNotFound(bucketName)
-	} else if err != nil && strings.Contains(err.Error(), api.ErrObjectNotFound.Error()) {
+	} else if utils.IsErr(err, api.ErrObjectNotFound) {
 		return nil, gofakes3.KeyNotFound(objectName)
 	} else if err != nil {
 		return nil, gofakes3.ErrorMessage(gofakes3.ErrInternal, err.Error())
@@ -298,7 +299,7 @@ func (s *s3) HeadObject(ctx context.Context, bucketName, objectName string) (*go
 	res, err := s.w.HeadObject(ctx, bucketName, objectName, api.HeadObjectOptions{
 		IgnoreDelim: true,
 	})
-	if err != nil && strings.Contains(err.Error(), api.ErrObjectNotFound.Error()) {
+	if utils.IsErr(err, api.ErrObjectNotFound) {
 		return nil, gofakes3.KeyNotFound(objectName)
 	} else if err != nil {
 		return nil, gofakes3.ErrorMessage(gofakes3.ErrInternal, err.Error())
@@ -346,9 +347,9 @@ func (s *s3) HeadObject(ctx context.Context, bucketName, objectName string) (*go
 //	isn't a null version, Amazon S3 does not remove any objects.
 func (s *s3) DeleteObject(ctx context.Context, bucketName, objectName string) (gofakes3.ObjectDeleteResult, error) {
 	err := s.b.DeleteObject(ctx, bucketName, objectName, api.DeleteObjectOptions{})
-	if err != nil && strings.Contains(err.Error(), api.ErrBucketNotFound.Error()) {
+	if utils.IsErr(err, api.ErrBucketNotFound) {
 		return gofakes3.ObjectDeleteResult{}, gofakes3.BucketNotFound(bucketName)
-	} else if err != nil && !strings.Contains(err.Error(), api.ErrObjectNotFound.Error()) {
+	} else if utils.IsErr(err, api.ErrObjectNotFound) {
 		return gofakes3.ObjectDeleteResult{}, gofakes3.ErrorMessage(gofakes3.ErrInternal, err.Error())
 	}
 
@@ -371,7 +372,7 @@ func (s *s3) PutObject(ctx context.Context, bucketName, key string, meta map[str
 	}
 
 	ur, err := s.w.UploadObject(ctx, input, bucketName, key, opts)
-	if err != nil && strings.Contains(err.Error(), api.ErrBucketNotFound.Error()) {
+	if utils.IsErr(err, api.ErrBucketNotFound) {
 		return gofakes3.PutObjectResult{}, gofakes3.BucketNotFound(bucketName)
 	} else if err != nil {
 		return gofakes3.PutObjectResult{}, gofakes3.ErrorMessage(gofakes3.ErrInternal, err.Error())
@@ -387,7 +388,7 @@ func (s *s3) DeleteMulti(ctx context.Context, bucketName string, objects ...stri
 	var res gofakes3.MultiDeleteResult
 	for _, objectName := range objects {
 		err := s.b.DeleteObject(ctx, bucketName, objectName, api.DeleteObjectOptions{})
-		if err != nil && !strings.Contains(err.Error(), api.ErrObjectNotFound.Error()) {
+		if err != nil && !utils.IsErr(err, api.ErrObjectNotFound) {
 			res.Error = append(res.Error, gofakes3.ErrorResult{
 				Key:     objectName,
 				Code:    gofakes3.ErrInternal,
diff --git a/stores/migrations.go b/stores/migrations.go
index 6395b52bb..b0304090e 100644
--- a/stores/migrations.go
+++ b/stores/migrations.go
@@ -3,9 +3,9 @@ package stores
 import (
 	"errors"
 	"fmt"
-	"strings"
 
 	"github.com/go-gormigrate/gormigrate/v2"
+	"go.sia.tech/renterd/internal/utils"
 	"go.uber.org/zap"
 	"gorm.io/gorm"
 )
@@ -32,7 +32,7 @@ func performMigrations(db *gorm.DB, logger *zap.SugaredLogger) error {
 			ID: "00002_prune_slabs_trigger",
 			Migrate: func(tx *gorm.DB) error {
 				err := performMigration(tx, dbIdentifier, "00002_prune_slabs_trigger", logger)
-				if err != nil && strings.Contains(err.Error(), errMySQLNoSuperPrivilege.Error()) {
+				if utils.IsErr(err, errMySQLNoSuperPrivilege) {
 					logger.Warn("migration 00002_prune_slabs_trigger requires the user to have the SUPER privilege to register triggers")
 				}
 				return err
diff --git a/worker/download.go b/worker/download.go
index 3a58bbc98..6f070acbd 100644
--- a/worker/download.go
+++ b/worker/download.go
@@ -7,13 +7,13 @@ import (
 	"fmt"
 	"io"
 	"math"
-	"strings"
 	"sync"
 	"time"
 
 	rhpv2 "go.sia.tech/core/rhp/v2"
 	"go.sia.tech/core/types"
 	"go.sia.tech/renterd/api"
+	"go.sia.tech/renterd/internal/utils"
 	"go.sia.tech/renterd/object"
 	"go.sia.tech/renterd/stats"
 	"go.uber.org/zap"
@@ -454,7 +454,7 @@ func (mgr *downloadManager) numDownloaders() int {
 // in the partial slab buffer.
 func (mgr *downloadManager) fetchPartialSlab(ctx context.Context, key object.EncryptionKey, offset, length uint32) ([]byte, *object.Slab, error) {
 	data, err := mgr.os.FetchPartialSlab(ctx, key, offset, length)
-	if err != nil && strings.Contains(err.Error(), api.ErrObjectNotFound.Error()) {
+	if utils.IsErr(err, api.ErrObjectNotFound) {
 		// Check if slab was already uploaded.
 		slab, err := mgr.os.Slab(ctx, key)
 		if err != nil {
diff --git a/worker/worker.go b/worker/worker.go
index dab8ef30a..99323b501 100644
--- a/worker/worker.go
+++ b/worker/worker.go
@@ -878,7 +878,7 @@ func (w *worker) objectsHandlerHEAD(jc jape.Context) {
 		IgnoreDelim:  ignoreDelim,
 		OnlyMetadata: true,
 	})
-	if err != nil && strings.Contains(err.Error(), api.ErrObjectNotFound.Error()) {
+	if utils.IsErr(err, api.ErrObjectNotFound) {
 		jc.Error(err, http.StatusNotFound)
 		return
 	} else if err != nil {
@@ -951,7 +951,7 @@ func (w *worker) objectsHandlerGET(jc jape.Context) {
 
 	path := jc.PathParam("path")
 	res, err := w.bus.Object(ctx, bucket, path, opts)
-	if err != nil && strings.Contains(err.Error(), api.ErrObjectNotFound.Error()) {
+	if utils.IsErr(err, api.ErrObjectNotFound) {
 		jc.Error(err, http.StatusNotFound)
 		return
 	} else if jc.Check("couldn't get object or entries", err) != nil {
@@ -1041,7 +1041,7 @@ func (w *worker) objectsHandlerPUT(jc jape.Context) {
 
 	// return early if the bucket does not exist
 	_, err = w.bus.Bucket(ctx, bucket)
-	if err != nil && strings.Contains(err.Error(), api.ErrBucketNotFound.Error()) {
+	if utils.IsErr(err, api.ErrBucketNotFound) {
 		jc.Error(fmt.Errorf("bucket '%s' not found; %w", bucket, err), http.StatusNotFound)
 		return
 	}
@@ -1160,7 +1160,7 @@ func (w *worker) multipartUploadHandlerPUT(jc jape.Context) {
 
 	// return early if the bucket does not exist
 	_, err = w.bus.Bucket(ctx, bucket)
-	if err != nil && strings.Contains(err.Error(), api.ErrBucketNotFound.Error()) {
+	if utils.IsErr(err, api.ErrBucketNotFound) {
 		jc.Error(fmt.Errorf("bucket '%s' not found; %w", bucket, err), http.StatusNotFound)
 		return
 	}
@@ -1263,7 +1263,7 @@ func (w *worker) objectsHandlerDELETE(jc jape.Context) {
 		return
 	}
 	err := w.bus.DeleteObject(jc.Request.Context(), bucket, jc.PathParam("path"), api.DeleteObjectOptions{Batch: batch})
-	if err != nil && strings.Contains(err.Error(), api.ErrObjectNotFound.Error()) {
+	if utils.IsErr(err, api.ErrObjectNotFound) {
 		jc.Error(err, http.StatusNotFound)
 		return
 	}
@@ -1563,5 +1563,5 @@ func isErrHostUnreachable(err error) bool {
 }
 
 func isErrDuplicateTransactionSet(err error) bool {
-	return err != nil && strings.Contains(err.Error(), modules.ErrDuplicateTransactionSet.Error())
+	return utils.IsErr(err, modules.ErrDuplicateTransactionSet)
 }