diff --git a/backend/mem_backend.go b/backend/mem_backend.go
index 9ba17a72f..21d78846b 100644
--- a/backend/mem_backend.go
+++ b/backend/mem_backend.go
@@ -125,6 +125,11 @@ func memCreate(be *MemoryBackend) (Blob, error) {
 	return blob, nil
 }
 
+// ReadCloser wraps a reader and adds a noop Close method.
+func ReadCloser(rd io.Reader) io.ReadCloser {
+	return readCloser{rd}
+}
+
 // readCloser wraps a reader and adds a noop Close method.
 type readCloser struct {
 	io.Reader
diff --git a/checker/checker.go b/checker/checker.go
index 7064e56c9..ecd2ed626 100644
--- a/checker/checker.go
+++ b/checker/checker.go
@@ -1,13 +1,17 @@
 package checker
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
+	"io/ioutil"
 	"sync"
 
 	"github.com/restic/restic"
 	"github.com/restic/restic/backend"
+	"github.com/restic/restic/crypto"
 	"github.com/restic/restic/debug"
+	"github.com/restic/restic/pack"
 	"github.com/restic/restic/repository"
 )
 
@@ -335,7 +339,7 @@ type TreeError struct {
 }
 
 func (e TreeError) Error() string {
-	return fmt.Sprintf("%v: %d errors", e.ID.String(), len(e.Errors))
+	return fmt.Sprintf("tree %v: %v", e.ID.Str(), e.Errors)
 }
 
 type treeJob struct {
@@ -634,3 +638,105 @@ func (c *Checker) UnusedBlobs() (blobs backend.IDs) {
 func (c *Checker) OrphanedPacks() backend.IDs {
 	return c.orphanedPacks
 }
+
+// CountPacks returns the number of packs in the repository.
+func (c *Checker) CountPacks() uint64 {
+	return uint64(len(c.packs))
+}
+
+// checkPack reads a pack and checks the integrity of all blobs.
+func checkPack(r *repository.Repository, id backend.ID) error {
+	debug.Log("Checker.checkPack", "checking pack %v", id.Str())
+	rd, err := r.Backend().Get(backend.Data, id.String())
+	if err != nil {
+		return err
+	}
+
+	buf, err := ioutil.ReadAll(rd)
+	if err != nil {
+		return err
+	}
+
+	err = rd.Close()
+	if err != nil {
+		return err
+	}
+
+	unpacker, err := pack.NewUnpacker(r.Key(), bytes.NewReader(buf))
+	if err != nil {
+		return err
+	}
+
+	var errs []error
+	for i, blob := range unpacker.Entries {
+		debug.Log("Checker.checkPack", "  check blob %d: %v", i, blob.ID.Str())
+
+		plainBuf := make([]byte, blob.Length)
+		plainBuf, err = crypto.Decrypt(r.Key(), plainBuf, buf[blob.Offset:blob.Offset+blob.Length])
+		if err != nil {
+			debug.Log("Checker.checkPack", "  error decrypting blob %v: %v", blob.ID.Str(), err)
+			errs = append(errs, fmt.Errorf("blob %v: %v", i, err))
+			continue
+		}
+
+		hash := backend.Hash(plainBuf)
+		if !hash.Equal(blob.ID) {
+			debug.Log("Checker.checkPack", "  ID does not match, want %v, got %v", blob.ID.Str(), hash.Str())
+			errs = append(errs, fmt.Errorf("ID does not match, want %v, got %v", blob.ID.Str(), hash.Str()))
+			continue
+		}
+	}
+
+	if len(errs) > 0 {
+		return fmt.Errorf("pack %v contains %v errors: %v", id.Str(), len(errs), errs)
+	}
+
+	return nil
+}
+
+// ReadData loads all data from the repository and checks the integrity.
+func (c *Checker) ReadData(p *restic.Progress, errChan chan<- error, done <-chan struct{}) {
+	defer close(errChan)
+
+	p.Start()
+	defer p.Done()
+
+	worker := func(wg *sync.WaitGroup, in <-chan backend.ID) {
+		defer wg.Done()
+		for {
+			var id backend.ID
+			var ok bool
+
+			select {
+			case <-done:
+				return
+			case id, ok = <-in:
+				if !ok {
+					return
+				}
+			}
+
+			err := checkPack(c.repo, id)
+			p.Report(restic.Stat{Blobs: 1})
+			if err == nil {
+				continue
+			}
+
+			select {
+			case <-done:
+				return
+			case errChan <- err:
+			}
+		}
+	}
+
+	ch := c.repo.List(backend.Data, done)
+
+	var wg sync.WaitGroup
+	for i := 0; i < defaultParallelism; i++ {
+		wg.Add(1)
+		go worker(&wg, ch)
+	}
+
+	wg.Wait()
+}
diff --git a/checker/checker_test.go b/checker/checker_test.go
index 37d7f7a7b..99e89a22a 100644
--- a/checker/checker_test.go
+++ b/checker/checker_test.go
@@ -1,10 +1,13 @@
 package checker_test
 
 import (
+	"io"
+	"math/rand"
 	"path/filepath"
 	"sort"
 	"testing"
 
+	"github.com/restic/restic"
 	"github.com/restic/restic/backend"
 	"github.com/restic/restic/checker"
 	"github.com/restic/restic/repository"
@@ -24,13 +27,13 @@ func list(repo *repository.Repository, t backend.Type) (IDs []string) {
 	return IDs
 }
 
-func checkPacks(chkr *checker.Checker) (errs []error) {
+func collectErrors(f func(chan<- error, <-chan struct{})) (errs []error) {
 	done := make(chan struct{})
 	defer close(done)
 
 	errChan := make(chan error)
 
-	go chkr.Packs(errChan, done)
+	go f(errChan, done)
 
 	for err := range errChan {
 		errs = append(errs, err)
@@ -39,19 +42,20 @@ func checkPacks(chkr *checker.Checker) (errs []error) {
 	return errs
 }
 
-func checkStruct(chkr *checker.Checker) (errs []error) {
-	done := make(chan struct{})
-	defer close(done)
+func checkPacks(chkr *checker.Checker) []error {
+	return collectErrors(chkr.Packs)
+}
 
-	errChan := make(chan error)
+func checkStruct(chkr *checker.Checker) []error {
+	return collectErrors(chkr.Structure)
+}
 
-	go chkr.Structure(errChan, done)
-
-	for err := range errChan {
-		errs = append(errs, err)
-	}
-
-	return errs
+func checkData(chkr *checker.Checker) []error {
+	return collectErrors(
+		func(errCh chan<- error, done <-chan struct{}) {
+			chkr.ReadData(nil, errCh, done)
+		},
+	)
 }
 
 func TestCheckRepo(t *testing.T) {
@@ -204,3 +208,102 @@ func TestDuplicatePacksInIndex(t *testing.T) {
 
 	})
 }
+
+// errorBackend randomly modifies data after reading.
+type errorBackend struct {
+	backend.Backend
+}
+
+func (b errorBackend) Get(t backend.Type, name string) (io.ReadCloser, error) {
+	rd, err := b.Backend.Get(t, name)
+	if err != nil {
+		return rd, err
+	}
+
+	if t != backend.Data {
+		return rd, err
+	}
+
+	return backend.ReadCloser(faultReader{rd}), nil
+}
+
+func (b errorBackend) GetReader(t backend.Type, name string, offset, length uint) (io.ReadCloser, error) {
+	rd, err := b.Backend.GetReader(t, name, offset, length)
+	if err != nil {
+		return rd, err
+	}
+
+	if t != backend.Data {
+		return rd, err
+	}
+
+	return backend.ReadCloser(faultReader{rd}), nil
+}
+
+// induceError flips a bit in the slice.
+func induceError(data []byte) {
+	if rand.Float32() < 0.8 {
+		return
+	}
+
+	pos := rand.Intn(len(data))
+	data[pos] ^= 1
+}
+
+// faultReader wraps a reader and randomly modifies data on read.
+type faultReader struct {
+	rd io.Reader
+}
+
+func (f faultReader) Read(p []byte) (int, error) {
+	n, err := f.rd.Read(p)
+	if n > 0 {
+		induceError(p)
+	}
+
+	return n, err
+}
+
+func TestCheckerModifiedData(t *testing.T) {
+	be := backend.NewMemoryBackend()
+
+	repo := repository.New(be)
+	OK(t, repo.Init(TestPassword))
+
+	arch := restic.NewArchiver(repo)
+	_, id, err := arch.Snapshot(nil, []string{"."}, nil)
+	OK(t, err)
+	t.Logf("archived as %v", id.Str())
+
+	checkRepo := repository.New(errorBackend{be})
+	OK(t, checkRepo.SearchKey(TestPassword))
+
+	chkr := checker.New(checkRepo)
+
+	hints, errs := chkr.LoadIndex()
+	if len(errs) > 0 {
+		t.Fatalf("expected no errors, got %v: %v", len(errs), errs)
+	}
+
+	if len(hints) > 0 {
+		t.Errorf("expected no hints, got %v: %v", len(hints), hints)
+	}
+
+	errFound := false
+	for _, err := range checkPacks(chkr) {
+		t.Logf("pack error: %v", err)
+	}
+
+	for _, err := range checkStruct(chkr) {
+		t.Logf("struct error: %v", err)
+	}
+
+	for _, err := range checkData(chkr) {
+		t.Logf("struct error: %v", err)
+		errFound = true
+	}
+
+	if !errFound {
+		t.Fatal("no error found, checker is broken")
+	}
+}
diff --git a/cmd/restic/cmd_check.go b/cmd/restic/cmd_check.go
index c3ba1dd83..8c59c2ffe 100644
--- a/cmd/restic/cmd_check.go
+++ b/cmd/restic/cmd_check.go
@@ -4,7 +4,11 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"time"
 
+	"golang.org/x/crypto/ssh/terminal"
+
+	"github.com/restic/restic"
 	"github.com/restic/restic/checker"
 )
 
@@ -29,6 +33,37 @@ func (cmd CmdCheck) Usage() string {
 	return "[check-options]"
 }
 
+func (cmd CmdCheck) newReadProgress(todo restic.Stat) *restic.Progress {
+	if !cmd.global.ShowProgress() {
+		return nil
+	}
+
+	readProgress := restic.NewProgress(time.Second)
+
+	readProgress.OnUpdate = func(s restic.Stat, d time.Duration, ticker bool) {
+		status := fmt.Sprintf("[%s] %s  %d / %d items",
+			formatDuration(d),
+			formatPercent(s.Blobs, todo.Blobs),
+			s.Blobs, todo.Blobs)
+
+		w, _, err := terminal.GetSize(int(os.Stdout.Fd()))
+		if err == nil {
+			if len(status) > w {
+				max := w - len(status) - 4
+				status = status[:max] + "... "
+			}
+		}
+
+		fmt.Printf("\x1b[2K%s\r", status)
+	}
+
+	readProgress.OnDone = func(s restic.Stat, d time.Duration, ticker bool) {
+		fmt.Printf("\nduration: %s\n", formatDuration(d))
+	}
+
+	return readProgress
+}
+
 func (cmd CmdCheck) Execute(args []string) error {
 	if len(args) != 0 {
 		return errors.New("check has no arguments")
@@ -109,6 +144,20 @@ func (cmd CmdCheck) Execute(args []string) error {
 		}
 	}
 
+	if cmd.ReadData {
+		cmd.global.Verbosef("Read all data\n")
+
+		p := cmd.newReadProgress(restic.Stat{Blobs: chkr.CountPacks()})
+		errChan := make(chan error)
+
+		go chkr.ReadData(p, errChan, done)
+
+		for err := range errChan {
+			errorsFound = true
+			fmt.Fprintf(os.Stderr, "%v\n", err)
+		}
+	}
+
 	if errorsFound {
 		return errors.New("repository contains errors")
 	}