Because the plaintiff, also defendant in counterclaim, believed that his landlord wrongfully held his security deposit in violation of G. L. c. 186, § 15, he opted, pro se, for the “simple, prompt, and informal means, at small expense, for adjudication of [his] claim[j” in the small claims session of the Boston Municipal Court. McLaughlin v. Levenbaum, 248 Mass. 170, 175-176 (1924). See G. L. c. 218, §§ 21-25. The defendant, seeking three months of rent in damages for the plaintiffs alleged breach of his written lease of the apartment, filed a counterclaim as permitted by Uniform Small Claims Rule 3(c) (1983).1

*46There was a hearing before a judge, who found in favor of the defendant (the landlord) on the original action and against the plaintiff (the tenant) on the counterclaim, and a judgment for $635 was entered. The plaintiff appealed the decision of the judge on the counterclaim to the jury session of the Boston Municipal Court pursuant to the second sentence of the second paragraph of G. L. c. 218, § 23, as amended through St. 1986, c. 295.2 A judge assigned to the six-member jury session dismissed the appeal on the ground that the plaintiff had no right to appeal. From that order the plaintiff now appeals.3

We have found no case expressly addressing the issue whether a small claims plaintiff, who opts for the small claims court and loses on a counterclaim, is deemed to have waived his right to a jury trial on that counterclaim.4

Normally a plaintiff who elects the small claims procedure waives any right to a trial by jury on the principal claim, unless the defendant claims an appeal to the six-person jury in the District or Municipal Court under G. L. c. 218, § 23. In contrast, a small claims defendant has a right to a jury *47trial on the claim initially asserted by the plaintiff, and that right is not altered by a defendant’s decision to bring a counterclaim in the small claims court.

We are of opinion that the right to trial by jury, as set forth in art. 15 of the Declaration of Rights of the Massachusetts Constitution, or as given by statute, does apply to a small claims plaintiff as a defendant in counterclaim.5 “In civil cases, waiver of a fundamental constitutional right is never presumed (Aetna Ins. Co. v. Kennedy, 301 U.S. 389, 393 [1937] [jury trial]), and always requires an intentional relinquishment of a known right or privilege. See Metropolitan Transit Auth. v. Railway Express Agency, Inc., 323 Mass. 707, 709 (1949).” Spence v. Reeder, 382 Mass. 398, 411-412 (1981). General Laws c. 218, § 23, explicitly prescribes a waiver of a jury trial for any plaintiff beginning a case under the small claims procedure. See note 2, supra. But in the counterclaim situation, there is no basis, express or otherwise, upon which to infer a waiver of a right to a jury trial, especially where the rules applicable in the small claims court permit the assertion of any counterclaims within that court’s jurisdiction. The only possible way to construe such a waiver on a counterclaim is to contend that the invocation of the small claims procedure, in and of itself, triggers such a waiver. Contrast Matsushita Elec. Corp. of Am. v. Sonus Corp., 362 Mass. 246, 252-253 (1972).

Such a conclusion is not supported by the language of the statute, nor, in our view, is it logical. The term “defendant” as used in § 23 includes a defendant in counterclaim. More importantly, were we to decide that such a decision amounts to a waiver, it would place every potential small claims plaintiff in the inappropriate dilemma of weighing the efficiency of the small claims procedure against the possibility of losing *48the right to a jury trial on any claim a defendant might elect to assert by way of counterclaim.

For these reasons, we hold that the plaintiff did not waive his right to a jury trial on the counterclaim asserted against him. The order dismissing the appeal to the Boston Municipal Court jury session is vacated and the counterclaim is remanded to that court for trial.

So ordered.