delivered the opinion of the court:
Defendant, Marty Glenn Stover, was charged by information with the crimes of burglary, theft and resisting or obstructing peace officers. The burglary and theft charges were dismissed prior to trial. A jury in the circuit court of *192Champaign County found defendant guilty of the offense of resisting or obstructing a peace officer in violation of section 31 — 1 of the Criminal Code of 1961 (Ill. Rev. Stat. 1979, ch. 38, par. 31—1). The appellate court reversed and remanded for a new trial (92 Ill. App. 3d 542), holding that a defense witness, who is a former codefendant, was improperly impeached by the use of his guilty plea to the same offense for which defendant was being tried. The court further held that the prosecutor’s inquiry into defendant’s previous acquaintance with the arresting officer was error. We allowed the State leave to appeal.
Two issues are raised on appeal: (1) May a witness be impeached by evidence that he pleaded guilty to the same misdemeanor offense with which defendant is charged? (2) Was it error for the prosecutor to inquire into defendant’s previous acquaintance with the arresting officer?
On October 10, 1979, police officers Doty, Thurman and Wolfe went to defendant’s apartment to arrest him and his brother, Randy. Deputy Doty was dressed in his official uniform, and Investigator Thurman wore plain clothes. The record is silent as to the attire of Deputy Wolfe.
There is conflicting evidence as to what occurred during the course of the arrest. The officers testified that they announced their purpose prior to entering the apartment. They further stated that defendant ran to the rear of the apartment, at which time Doty pursued him and attempted to handcuff him. A scuffle ensued, during which the officer “kneed” the defendant in the chest area. Defendant eventually ceased resistance.
At the conclusion of Doty’s direct examination, he described in detail the outfit he wore on the day of defendant’s arrest. He testified that he had on his uniform, an official hat, and a number of badges identifying him as a deputy sheriff. Further, he stated that he was wearing an equipment belt which contained a holster and weapon, handcuffs, and a nightstick. After eliciting this testimony, *193the prosecutor asked Doty whether he had been acquainted with the defendant prior to this incident. An objection to the question was overruled, and Doty responded “yes.”
Defendant’s testimony indicated that he did not resist Doty. He claimed that he was walking toward the rear of the apartment to leave for his mother’s nearby residence and consult her about the matter. Doty allegedly followed him into the kitchen, pushed him up against the wall, and handcuffed him.
Randy Stover also testified for the defense. During cross-examination, he stated that he was not told he was under arrest prior to being handcuffed. The prosecutor then asked if he pleaded guilty to a resisting-arrest charge arising out of the same incident. Defendant objected, and the court requested a side-bar conference. Thereafter, the judge overruled the objection. The grounds upon which defendant objected are not disclosed in the record. Following the judge’s ruling, Randy admitted that he entered a guilty plea to the charge. The prosecutor then asked if he had not just told the jury that he was never informed he was arrested. Defendant objected on the basis that the question was asked and answered. The objection was overruled, and Randy responded “yes.” During closing argument, the State emphasized the alleged inconsistency between Randy’s testimony and his prior guilty plea.
The jury found defendant guilty of resisting or obstructing Deputy Doty, but not guilty of resisting Investigator Thurman, who had been dressed in plain clothes. Defendant was sentenced to one year’s probation, with the condition that he spend 15 weekends in jail and pay a $100 fine and court costs.
A threshold question concerns the reviewability of defendant’s contention that his brother was improperly impeached with evidence of his prior guilty plea. As noted earlier, defendant objected to this testimony, but the record is silent as to the reason. However, the specific ground for *194the objection was included in his post-trial motion. A primary purpose of the post-trial motion is to allow trial judges an opportunity to consider the litigants’ arguments and assess his rulings. (People v. Adkisson (1980), 83 Ill. 2d 1, 7-8; Brown v. Decatur Memorial Hospital (1980), 83 Ill. 2d 344, 349-50.) Since the alleged error may have been specifically asserted at the unrecorded side-bar conference and was specifically stated in the post-trial motion, we do not find that the objection was waived. See People v. Lykins (1979), 77 Ill. 2d 35, 38; People v. Precup (1978), 73 Ill. 2d 7, 19.
Defendant relies on People v. Montgomery (1971), 47 Ill. 2d 510, for the proposition that a codefendant cannot be impeached by evidence that he was convicted of a misdemeanor which does not involve dishonesty. In Montgomery, this court adopted proposed Federal Rule of Evidence 609 as the standard governing impeachment by evidence of a prior conviction. Although a slightly different version of Rule 609 was ultimately adopted for use in the Federal courts, we have adhered to the rule as originally proposed. (See People v. Spates (1979), 77 Ill. 2d 193, 200; Knowles v. Panopoulos (1977), 66 Ill. 2d 585, 587-88.) This rule provides, in relevant part (Proposed Fed. R. Evid. 609(a)):
“For the purpose of attacking the credibility of a witness, evidence that he has been convicted of a crime, except on a plea of nolo contendere, is admissible but only if the crime, (1) was punishable by death or imprisonment in excess of one year under the law under which he was convicted, or (2) involved dishonesty or false statement regardless of the punishment unless (3), in either case, the judge determines that the probative value of the evidence of the crime is substantially outweighed by the danger of unfair prejudice.” (47 Ill. 2d 510, 516.)
In the instant case, there is no question that the conviction fails to meet either test enunciated in Montgomery. Resisting or obstructing a peace officer is a misdemeanor which *195clearly does not involve dishonesty or a false statement.
The State, however, contends that the Montgomery decision is inapplicable because evidence of the guilty plea has relevance independent of its use as a prior conviction. Relying on People v. Sullivan (1978), 72 Ill. 2d 36, it argues that the guilty plea should be admissible for impeachment purposes as a prior inconsistent statement.
In Sullivan, it was recognized that evidence that a codefendant pleaded guilty to the same offense for which defendant stands trial is admissible for purposes of impeaching the codefendant. (72 Ill. 2d 36, 42; see Annots., 48 A.L.R.2d 1004 & 1016 (1956), and cases cited therein.) This principle, considered within the context of the case, related to impeachment by a prior conviction, and merely articulates the holding in People v. Montgomery (1971), 47 Ill. 2d 510. The guilty plea involved in Sullivan related to a felony offense, which is otherwise admissible for impeachment purposes. Thus, this case does not support the State’s contention that a guilty plea, inadmissible under Montgomery as evidence of a prior conviction, may nevertheless be admissible as a prior inconsistent statement.
“A defendant who is separately tried is entitled to have his guilt or innocence determined upon the evidence against him without being prejudged according to what has happened to another.” (People v. Sullivan (1978), 72 Ill. 2d 36, 42.) Although a witness’ prior convictions may be admissible to attack his credibility, admissibility is limited to the defined standards set forth in proposed Federal Rule 609. The State should not be allowed to circumvent this rule by labeling a guilty plea as evidence of a prior inconsistent statement. To condone this practice would virtually eviscerate the Montgomery holding.
Further, the jury was not cautioned to disregard the improper evidence. Indeed, the prosecutor consistently emphasized, in his closing argument, that defendant’s brother pleaded guilty to the offense in question. The implication *196was that defendant’s guilt could be gauged accordingly. Under like circumstances, it has been held that evidence of a codefendant’s guilty plea constituted reversible error. (People v. Sullivan (1978), 72 Ill. 2d 36.) Similarly, it cannot be said here that the erroneous admission of the evidence did not prejudice defendant’s case. We therefore hold that, under these circumstances, evidence of the witness’ prior guilty plea constituted reversible error, entitling the defendant to a new trial. See People v. Godsey (1978), 74 Ill. 2d 64, 73.
The final issue relates to the prosecutor’s inquiry into defendant’s previous acquaintance with the arresting officer. The State first contends that the question was probative of the issue of defendant’s knowledge that Doty was a police officer. Since knowledge is an essential element of the offense charged, it is argued that the deputy’s testimony was relevant. However, as defendant asserts, his knowledge of Doty’s status was already clearly established. The police officer testified at length as to his official attire on the day of the arrest. Therefore, defendant’s knowledge was no longer at issue.
The State next argues that the question did not provide a basis from which the jury could infer that defendant had previously engaged in illegal conduct. It has been held that evidence that the arresting officer was previously acquainted with defendant does not necessarily imply a criminal record. (People v. Rogers (1940), 375 Ill. 54, 59.) However, under the circumstances of this case, there is no apparent reason why the prosecutor would inquire into defendant’s previous acquaintance with Doty unless an implication of prior criminal activity was intended. We trust that on retrial such inquiry will not recur.
For the reasons stated herein, the appellate court judgment is affirmed.