@@ -215,7 +215,7 @@ func isValidParent(img, parent *image.Image) bool {

 	if len(parent.History) >= len(img.History) {

 		return false

 	}

-	if len(parent.RootFS.DiffIDs) >= len(img.RootFS.DiffIDs) {

+	if len(parent.RootFS.DiffIDs) > len(img.RootFS.DiffIDs) {

 		return false

 	}

@@ -7081,6 +7081,27 @@ func (s *DockerSuite) TestBuildWithFailure(c *check.C) {

 	c.Assert(stdout, checker.Not(checker.Contains), "Step 2/2 : RUN nobody")

 }

+func (s *DockerSuite) TestBuildCacheFromEqualDiffIDsLength(c *check.C) {

+	dockerfile := `

+		FROM busybox

+		RUN echo "test"

+		ENTRYPOINT ["sh"]`

+	ctx, err := fakeContext(dockerfile, map[string]string{

+		"Dockerfile": dockerfile,

+	})

+	c.Assert(err, checker.IsNil)

+	defer ctx.Close()

+

+	id1, err := buildImageFromContext("build1", ctx, true)

+	c.Assert(err, checker.IsNil)

+

+	// rebuild with cache-from

+	id2, out, err := buildImageFromContextWithOut("build2", ctx, true, "--cache-from=build1")

+	c.Assert(err, checker.IsNil)

+	c.Assert(id1, checker.Equals, id2)

+	c.Assert(strings.Count(out, "Using cache"), checker.Equals, 2)

+}

+

 func (s *DockerSuite) TestBuildCacheFrom(c *check.C) {

 	testRequires(c, DaemonIsLinux) // All tests that do save are skipped in windows

 	dockerfile := `