Robert T. Griffith, Appellant, vs. Dean A. Jackson, Respondent, Susan Donnelly, Respondent.

may not be cited except as provided by

Minn. Stat. § 480 A. 08, subd. 3 (1996).

 STATE OF MINNESOTA

 IN COURT OF APPEALS

 CX-97-2329

Robert T. Griffith,

Appellant,

vs.

Dean A. Jackson,

Respondent,

Susan Donnelly,

Respondent.

 Filed June 30, 1998

 Reversed and Remanded

 Shumaker, Judge

Hennepin County District Court

977893

Bruce R. Rubbelke, Nicklaus Law Firm, 103 West Second Street, P.O. Box 116, Chaska, MN 55318 (for appellant)

Dean A. Jackson and Susan Donnelly, 4233 Kentucky Avenue, Crystal, MN 55428 (pro se respondents)

Considered and decided by Peterson, Presiding Judge, Amundson, Judge, Shumaker, Judge.

 U N P U B L I S H E D O P I N I O N

 SHUMAKER, Judge

Appellant Robert T. Griffith appeals from a judgment based on a finding that his action to recover allegedly past due rents is barred by the statute of limitations. He contends that the district court erred in applying the statute of limitations because the respondents never raised the statute as a defense to the action. We reverse and remand.

 FACTS

Respondents rented a house from appellant from November 15, 1987 until September 30, 1991. The first four and one-half months of the tenancy was governed by a written lease that provided for automatic successive lease renewals for terms of one year each. Respondents could terminate the lease at any time by giving "two pay periods" advance written notice of their intention to do so. Respondents gave written notice by mail of their intent to vacate on or about August 1, 1991, and they moved from the premises at the end of September 1991.

In early February 1997, appellant filed a conciliation court claim against respondents in the sum of $7,250.45 for "rent owed and exterior damage to house." The district administrator mailed a "Summons - Notice of Hearing" to respondents on February 11, 1997. After hearing, the conciliation court awarded $800 to appellant, who then removed the action to the district court for trial de novo.

At trial, appellant sought to recover $3,465 as rent for March and September 1989, April, July, and November 1990, and February and October 1991; $1,324.95 as interest on past due rents; $480 for late fees under the written lease; $2,250 for loss of awnings on the premises; and $607.50 in attorney fees as required by the written lease. Respondents contended that they had paid some of the rent in appellant's claim, had compromised a potential injury claim against appellant as to the remainder of the rent, and had disposed of the awnings with appellant's consent. They argued that they owed appellant nothing.

The district court concluded that appellant failed effectively to renew the written lease and that the tenancy was converted by law to month-to-month from April 1, 1988 until September 30, 1991. The district court also ruled that respondents had paid rents due for March and September 1989 and April 1990; had properly terminated their tenancy as of September 30, 1991 and, thus, owed no rent for October 1991; and had disposed of the awnings with appellant's consent, so that it was improper for appellant to apply respondent's security deposit of $425 to the loss of the awnings. Finally, the district court ruled that remaining claims for rent and related damages for any time prior to February 1991 were barred by the statute of limitations. Appellant challenges the district court's application of the statute of limitations.

 D E C I S I O N

This court will reverse the district court's factual findings only if a review of the entire evidence leaves us with "the definite and firm conviction that a mistake has been made." In re Guardianship of Dawson, 502 N.W.2d 65, 68 (Minn. App. 1993) (quoting Gjovik v. Strope, 401 N.W.2d 664, 667 (Minn. 1987)), review denied (Minn. Aug. 16, 1993). This appeal raises issues of law and of fact. We review questions of law de novo. Frost-Benco Elec. Ass'n. v. Minnesota Pub. Utils. Comm'n., 358 N.W.2d 639, 642 (Minn. 1984).

Appellant argues that the district court erred by applying the statute of limitations when the respondents never raised that defense. The statute of limitations is an affirmative defense. Minn. R. Civ. P. 8.03. It must be pleaded specifically or it is waived. Melbo v. Rinn, 280 Minn. 72, 74, 157 N.W.2d 842, 844, n. 1 (1968). The primary purpose of pleadings is to give to parties notice of claims and defenses so that they can prepare their proof accordingly. Conley v. Gibson, 355 U.S. 41, 47, 78 S. Ct. 99, 103 (1957); Roberge v. Cambridge Coop. Creamery Co., 243 Minn. 230, 232, 67 N.W.2d 400, 402 (1954); Rogers v. Drewry, 196 Minn. 16, 19, 264 N.W. 225, 226 (1935). Conciliation court rules do not require an answer to a claim. Minn. R. Gen. Pract. 507. Pleadings are not required upon removal to district court but they are permitted. Minn. R. Gen. Pract. 522.

Respondents did not raise the defense of the statute of limitations in any manner. They filed no pleading nor did they raise the issue orally at the de novo trial. Rather, the district court in its findings applied the statute sua sponte. This was error. There appears to be no Minnesota case on point, but the weight of authority from other jurisdictions supports the conclusion that the trial court cannot sua sponte assert an affirmative defense on behalf of a litigant. See Estabrook v. Baden, 943 P.2d 1334, 1336 (Mont. 1997) (if party fails to raise statute of limitations defense, defense is waived and cannot be raised sua sponte by court); Smith v. Rheaume, 623 So. 2d 625, 626 (Fla. Dist. Ct. App. 1993) (interpreting rule identical with Minnesota 8.03, appellant court held defendant may raise or waive statute of limitations as affirmative defense, but court cannot do so). See also Davis v. Bryan, 810 F.2d 42, 44 (2d Cir. 1987); Wagner v. Fawcett Publications, 307 F.2d 409, 412 (7th Cir. 1962) cert. denied 372 U.S. 909, 83 S. Ct. 723 (1963); Feldman v. Gogos, 628 A.2d 103, 105 (D.C. 1993); Adams v. Inman, 892 S.W.2d 651, 653 (Mo. Ct. App. 1994). When a trial court in its findings relies on a statute of limitations defense that had not been raised by a defendant, it deprives the plaintiff of the notice that is the reason for the rules of pleading.

The district court's findings and conclusions with respect to the expiration of the written lease, the notice of termination of the tenancy, the payment of rent for March and September 1989 and August 1990, and the disposal of the awnings involve credibility issues and are supported by the evidence. Thus, the appellant is entitled to rents for July and November 1990 and February 1991, at the rate of $495 each month, with statutory interest. Respondents are entitled to a set-off in an amount equal to their security deposit of $425 plus statutory interest from the lease's inception on November 15, 1987. Because the basis for the late fees and attorney fees was the written lease that expired prior to any default, appellant is not entitled to recover for those items.

We reverse and remand for entry of judgment calculated in accordance with this opinion.

  Reversed and remanded.