Petitioner appeals from the judgment denying his petition for post-conviction relief in which he claimed, inter alia, that he had received ineffective assistance of counsel due to trial counsel’s failure to object to the trial court’s answer to an inquiry from the jury in his criminal case. We conclude that the trial court’s answer to the jury’s inquiry about the elements of the crime of conspiracy was ambiguous and, because of its ambiguity, could have misled the jury. Trial counsel’s failure to object to the ambiguous answer prejudiced petitioner in that the jury could have convicted him even though the state had failed to prove that petitioner intended to commit the criminal act. that was the subject of the conspiracy, an element of the crime of conspiracy. Accordingly, we reverse the judgment of the post-conviction court.
Petitioner was charged with three counts of conspiracy to commit murder and aggravated murder. ORS 161.450; ORS 163.095(2)(a)(A); ORS 163.115. The trial court instructed the jury:
“Oregon law provides that a person commits the crime of conspiracy if the person, with the intent to commit a crime, agrees with one or more persons to commit the crime. To establish the crime of conspiracy to commit the crime of aggravated murder or murder, the State must prove beyond a reasonable doubt the following four elements.
“First, the crime of conspiracy occurred in Josephine County, Oregon. Two, the crime of conspiracy occurred between April 1st, 1988 and September 30th, 1989. Three, that George Oliver Jones with intent to commit the crime of aggravated murder or murder, four, agree with William Rice to commit the crime of aggravated murder of William Arnado or the murder of William Arnado or Roger Wirth.
“The crime of conspiracy is complete when the conspiratorial agreement is entered into with the intent to commit aggravated murder or murder. The unlawful agreement and not its accomplishment is the essence of the crime.”1
*510(Emphasis added.) During deliberations, the jury submitted a note to the court, reading as follows:
“We are having some dispute as to the definition of the word ‘intent.’ Is the defendant guilty of conspiracy if he did indeed make a plan with others to kill or must it be proved that the defendant was definitely serious, and fully intended to go through with the plan?”
(Emphasis added.) In an off-the-record meeting with counsel for the state and petitioner,2 the trial court decided to give the following answer:
“The court has reviewed your question and would submit the following answer. Your question is a two-part question. The answer to part one is yes and the answer to part two is yes.”
(Emphasis added.) The jury then convicted petitioner on all counts. His conviction was affirmed on appeal. State v. Jones, 126 Or App 224, 868 P2d 18, rev den 318 Or 583 (1994).
In a post-conviction relief proceeding, the petitioner has the burden of proving the allegations in the petition by a preponderance of the evidence. ORS 138.620(2). To establish inadequate assistance of counsel under the Oregon Constitution, a petitioner must prove that counsel failed to do the things reasonably necessary to advance the petitioner’s defense and that the petitioner suffered prejudice as a result. Stevens v. State of Oregon, 322 Or 101, 108, 902 P2d 1137 (1995). Under the Sixth and Fourteenth Amendments to the United States Constitution, denial of adequate assistance of counsel is demonstrated when a petitioner shows that counsel’s performance was deficient and that the deficient performance prejudiced the defense. Strickland v. Washington, 466 US 668, 687, 104 S Ct 2052, 80 L Ed 2d 674 (1984). In other words, petitioner faces a two-pronged test. He must prove that his counsel failed to exercise reasonable professional skill and judgment, and he must prove prejudice as a result of that failure. Davis v. Armenakis, 151 Or App 66, 69, 948 P2d 327 (1997), rev den 328 Or 194 (1998).
*511Petitioner argues that both the trial court and the post-conviction court misunderstood the import of the jury’s question. He contends that, on receipt of the answer, jurors could have decided to convict him based solely on the court’s answer to the first part of the question, even though some members of the jury did not believe that he intended to go through with the planned act. The state argues in response that, when the answer is viewed in its entirety, the answer to the first part is necessarily subsumed by the answer to the second:
“To the extent the jury’s note can be interpreted to be an either/or question, the trial court’s answer ‘The answer to part one is yes, and. the answer to part two is yes’ (emphasis added) — plainly indicates that a finding of guilt required an affirmative finding to both questions; indeed, the jury logically could not find that [petitioner] fully intended to go through with the plan without finding that he had made a plan.”
The problem with the state’s response is that it focuses solely on the answer to the jury’s question without considering the question to which it responded. The jury phrased its question in the disjunctive, so the only reasonable interpretation of its query was that it wanted to know whether it could convict petitioner if it found that he had merely agreed to a plan or whether it further had to find that he had intended to go through with it. The trial court’s answer, given in the conjunctive, was arguably accurate to the extent that it could be read to mean that the jury had to find both elements. However, that answer, viewed in the context of the jury’s question, was hopelessly ambiguous. Viewed in that context, the court’s answer was that the jury did not have to find that defendant intended to act on the plan in order to convict him of conspiracy and that it did have to find that he intended to act on the plan to do that.
An answer, such as the one at issue here, that affirms each of two mutually exclusive alternatives is nonsensical. We cannot pretend to know how jurors made sense of that illogical answer, and it is quite probable that different jurors understood the answer differently. Thus, members of the jury who believed that petitioner had made the agreement but had not really intended to kill anyone may well *512have been convinced by the court’s answer to the first part of their question to believe that the agreement alone was sufficient to support a conviction.
The dissent argues that the failure to object was a tactical decision that reasonable counsel could have made and, therefore, that it did not rise to the level of violating defendant’s right to effective assistance of counsel. However, aside from noting the answer’s succinctness, the dissent fails to explain how defendant could possibly have benefited from the inherently ambiguous answer. We decline to hold that reliance on incoherent jury instructions is a valid tactical decision. Relying on such instructions is more akin to entering a defendant’s fate into a lottery system than to making a rational decision about trial strategy.
Competent counsel would have recognized the fatal ambiguity in the court’s answer and would have called it to the court’s attention.3 Because petitioner’s counsel failed to do that, his performance was deficient. However, unless it can be shown that the defense was prejudiced, that deficiency is not sufficient to reverse the judgment of the post-conviction court. “Not all lapses of professional skill and judgment entitle a defendant to post-conviction relief. Instead, ‘only those acts or omissions by counsel which have a tendency to affect the result of the prosecution can be regarded as of constitutional magnitude^]’ ” Stevens, 322 Or at 110 (quoting Trujillo v. Maass, 312 Or 431-35, 822 P2d 703 (1991) (emphasis and brackets in original).
In this case, the prejudice is readily apparent. Petitioner’s defense was that, although he had engaged in conversations in which he had agreed to kill two people, it was all just “bar talk” and he never intended to kill anyone. It is possible that at least some members of the jury could have concluded that petitioner had entered into a superficial “agreement” but that he did not mean to kill anyone. Those *513jurors may, then, have leaned toward acquittal before receiving the court’s answer to their question. It is further possible that they believed that only the first part of the court’s answer applied to their concern and, therefore, that they ignored the second part.
That possibility is supported by a local news videotape and transcript that were admitted as evidence in the post-conviction case, in which jurors complain that they were confused by the trial court’s instructions and state that they now believed, based on the law of conspiracy, that the result should have been different.4 Although it is possible that the jurors were simply expressing second thoughts about their decision, akin to a buyer’s remorse, it is also possible that an already confused jury was made hopelessly confused by the ambiguous answer to its question. Competent counsel could have avoided that confusion, and the result of the case could well have been different. Accordingly, we conclude that petitioner was prejudiced by his counsel’s failure properly to object to the court’s answer.
*514Reversed and remanded with instructions to grant post-conviction relief.5
The jury received a written version of the instructions.
At trial, petitioner was represented by two attorneys, Farmer and Jesky. Neither petitioner nor Jesky was present when the jury’s question was discussed.
It is not difficult to formulate a simple, and correct, response to the jury’s question. The jury could have been told:
“The court answers your question as follows: To convict defendant of conspiracy, you must find that he made an agreement to commit the charged crimes and that he intended to perform the agreement.”
The transcript of the news report contains the following exchange:
“MASON [reporterl: [ Juror 1 Shoup says jurors were also confused about the question of intent when they asked the judge in a note if they had to be convinced that Jones was actually going to carry out the killing. The answer the judge wrote back was confusing.
“SHOUP: Boy, I honestly think that the outcome would have been just exactly the opposite had the judge explained it fully, because now I know the true answer to that question. I think we were given the wrong answer. Either that or—
“MASON: Shoup says some of the jurors were so confused that deliberations broke down. * * *
“MCFARLANE [jury forepersonl: I felt bad the moment we walked back in and I had to tell the judge that we the jury find the defendant guilty. I felt very bad.
“MASON: McFarlane says it was confusion over the judge’s handwritten note that caused him to switch from not guilty to guilty. And [thatl had the judge called the jury back in to the courtroom to explain fully that intent was necessary, he would have maintained his not guilty vote.”
While the news report supports the proposition that the ambiguous answer prejudiced defendant’s case, it is not necessary to rely on the report to find prejudice. As explained above, the trial court’s answer to the jury’s question was inherently ambiguous. More importantly., it was susceptible to a construction that was much less favorable to defendant than the law allows. Thus, the answer alone is sufficient to support a finding of prejudice.
Because of our disposition of this first issue, we need not reach petitioner’s other assignments of error.