@@ -2589,6 +2589,7 @@ func (cli *DockerCli) CmdExec(args ...string) error {

 	execConfig, err := runconfig.ParseExec(cmd, args)

 	if err != nil {

+		cmd.Usage()

 		return err

 	}

 	if execConfig.Container == "" {

@@ -351,3 +351,19 @@ func TestExecTtyWithoutStdin(t *testing.T) {

 	logDone("exec - forbid piped stdin to tty enabled container")

 }

+

+func TestExecParseError(t *testing.T) {

+	defer deleteAllContainers()

+

+	runCmd := exec.Command(dockerBinary, "run", "-d", "--name", "top", "busybox", "top")

+	if out, _, err := runCommandWithOutput(runCmd); err != nil {

+		t.Fatal(out, err)

+	}

+

+	// Test normal (non-detached) case first

+	cmd := exec.Command(dockerBinary, "exec", "top")

+	if out, _, err := runCommandWithOutput(cmd); err == nil || !strings.Contains(out, "Usage:") {

+		t.Fatalf("Should have thrown error & given usage: %s", out)

+	}

+	logDone("exec - error on parseExec should return usage")

+}