In the Matter of the Welfare of: A.P., C.P., & V.P.

may not be cited except as provided by

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

 STATE OF MINNESOTA

 IN COURT OF APPEALS

 CX-98-171

Penn Oak Apartments,

Respondent,

vs.

Leon Williams,

Appellant.

 Filed August 11, 1998

 Affirmed

Klaphake, Judge

Hennepin County District Court

File No. 1971208534

Gregory M. Miller, Donald A. Perron, Davis Dodd Levine & Miller, Ltd., 1219 Marquette Ave. S., Ste. 200, Minneapolis, MN 55403 (for respondent)

Leon Williams, P.O. Box 11851, Minneapolis, MN 55411 (appellant pro se)

Considered and decided by Crippen, Presiding Judge, Toussaint, Chief Judge, Klaphake, Judge.

 U N P U B L I S H E D O P I N I O N

 KLAPHAKE, Judge

Leon Williams appeals pro se from a judgment for restitution of premises in this unlawful detainer action, which alleges nonpayment of rent in December 1997 and nonpayment of accumulated past due rents and late fees for months prior to August 1997. We affirm for the following reasons: (1) this action is not barred by res judicata because a prior action involved nonpayment of rent for a different time period; (2) the trial court properly concluded that respondent Penn Oaks Apartments (Penn Oaks) did not waive its right to bring this unlawful detainer action by accepting rent payments from him for months prior to December 1997; and (3) Williams presented no evidence to support his claim of retaliatory eviction.

 D E C I S I O N

 I.

Williams argues that a November 14, 1997 decision in a prior unlawful detainer action bars this action because the claims now being asserted could have been brought in the prior action. See Dorso Trailer Sales, Inc. v. American Body & Trailer, Inc., 482 N.W.2d 771, 774 (Minn. 1992) (res judicata bars second action if party required to assert all alternative theories of recovery in initial action and party had full and fair opportunity to raise all alternative theories but failed to do so). Williams insists that because the current claims for past due rents and late fees accrued as early as July 1997, the two cases amount to inappropriate "serial evictions."

In the prior action, Penn Oaks alleged nonpayment of rent and late fees in the amount of $925 for part of August and all of September and October 1997. In denying possession to Penn Oaks, the trial court found that because Penn Oaks had failed to notify Williams of its existing accounting practice of applying any payments received to past due amounts, the payments Williams made in August, September, and October covered the rents for those months. Thus, the prior decision is only res judicata as to any unlawful detainer action based on nonpayment of rents due during the August-October 1997 period; it does not preclude this action for nonpayment of rent in December 1997.

 II.

Williams argues that Penn Oaks waived its right to evict him by accepting his monthly payments in August through November 1997. Generally, a landlord who accepts rent from a tenant waives the right to assert certain types of past defaults as a basis for an unlawful detainer action. Priordale Mall Investors v. Farrington, 411 N.W.2d 582, 585 (Minn. App. 1987) (landlord may waive right to assert known defaults of lease provisions). However, where nonpayment of rent involves a lease covenant that is part of the consideration and not "merely a covenant as to an incidental or collateral matter having to do with the character of the occupancy," no waiver occurs when a landlord accepts rent payments. Central Union Trust Co. v. Blank, 168 Minn. 312, 316, 210 N.W. 34, 35-36 (1926) (receipt of rent not waiver of right to terminate for nonpayment of taxes, which lease provided were to be paid "in lieu of additional rent"). Thus, the trial court did not err in concluding that there was no waiver in this case. See Westminster Corp. v. Anderson, 536 N.W.2d 340, 341 (Minn. App. 1995) (question of waiver presents de novo issue of law when facts undisputed), review denied (Minn. Oct. 27, 1995).

Williams also argues that Penn Oaks waived its rights under Minn. Stat. § 504.02, subd. 1(c) (1996), which requires a written non-waiver statement when a landlord attempts to evict a tenant in the same month for which partial payments are accepted. Because Penn Oaks never accepted a tender of rent for December, due to Williams's failure to satisfy first his past due amounts for the months prior to August, section 504.02 does not apply.

Williams further argues that Penn Oaks' November 17, 1997 written notice regarding its practice of applying any payments first to past due amounts was ineffective because the terms of an oral lease cannot be amended except on 30 days' notice. See Minn. Stat. § 504.06 (1996); Oesterreicher v. Robertson, 187 Minn. 497, 501, 245, N.W. 825, 826 (1932) (landlord or tenant wishing to terminate month-to-month tenancy must give month's notice of such intent). The trial court properly reasoned that the notice was effective when given because it merely informed Williams of a standard accounting practice and did not constitute a change in the terms of his oral lease. In addition, Williams received actual notice of Penn Oaks' accounting practice as early as October 14, 1997, when he was served with the first unlawful detainer complaint alleging nonpayment of rent for August through October; because Williams made payments during these months, he was put on notice that these payments were being credited to his past due amounts.

 III.

Williams argues that Penn Oaks' actions are retaliatory. See Parkin v. Fitzgerald, 307 Minn. 423, 428-29, 240 N.W.2d 828, 831 (1976) (under Minn. Stat. § 566.03, tenant may defend unlawful detainer action by establishing action brought in retaliation for good faith effort on tenant's part to enforce contractual or statutory rights). Williams did not testify at trial that Penn Oaks was motivated to evict him in retaliation for his assertion of any legal rights, nor did he present any other evidence to support this claim.

The judgment of restitution is affirmed.

Affirmed.