In this post-conviction relief case, we write only to address petitioner’s claim1 that his trial counsel2 was constitutionally inadequate because counsel failed to object to petitioner’s sentence under the Dangerous Offender Act (Act), ORS 161.725, on the ground that petitioner was entitled to a jury determination of whether the criminal act “seriously endangered the life or safety of another.” ORS 161.725(l)(b).
The material facts are undisputed. In 1987, a jury convicted petitioner for assault in the second degree, which is a Class B felony. ORS 163.175. At sentencing, the trial court determined that petitioner’s acts seriously endangered the life or safety of another and sentenced him as a dangerous offender. Petitioner’s trial counsel did not object to the trial court making that determination. The post-conviction court denied petitioner’s claim for relief. As to the issue here, the court based its ruling on the fact that State v. Mitchell, 84 Or App 452, 734 P2d 379 (1987), which established a defendant’s right to have a jury decide whether the criminal act seriously endangered another,3 “was handed down after petitioner’s conviction.” The court concluded: “When an argument is not well settled at law, trial counsel cannot be constitutionally inadequate for failing to make it.”
*161In determining whether representation was inadequate, we must evaluate whether counsel failed to “do those things reasonably necessary to diligently and conscientiously advance the defense.” Krummacher v. Gierloff, 290 Or 867, 874, 627 P2d 458 (1981). That determination includes an examination into whether counsel failed to raise reasonable issues at trial that were “fundamental” to a petitioner’s defense. Haynes v. State of Oregon, 121 Or App 395, 398-99, 854 P2d 949 (1993).
Here, petitioner argues that, notwithstanding Mitchell’s publication date, the precedent supporting Mitchell was well established and “should have alerted [trial] counsel to the premise articulated in Mitchell.” Petitioner further argues that, because trial counsel should have been aware of Mitchell’s premise, “[t]rial counsel had an obligation to raise this issue on petitioner’s behalf.” We agree.
The premise to which petitioner refers, the right to have a jury decide the elements of a crime, is secured by Article I, section 11, of the Oregon Constitution. The cases that established that premise and that support Mitchell are State v. Wedge, 293 Or 598, 652 P2d 773 (1982), and State v. Quinn, 290 Or 383, 623 P2d 630 (1981), both of which were decided at least five years before petitioner’s trial. In each case, the Supreme Court established a “simple principle” for distinguishing whether the inquiries into sentence enhancements are for the jury or for the court: “[T]he facts which constitute the crime are for the jury and those which characterize the defendant are for the sentencing court.” Quinn, 290 Or at 405; see also Wedge, 293 Or at 608 (holding that a determination of whether a defendant used a gun during a robbery, which enhanced the penalty, was for a jury to decide). Here, that principle’s application is clear.
Under the Act, the predicate determination for non-Class A felonies is whether the act “is a felony that seriously endangered the life or safety of another.” ORS 161.725(l)(b). As we explained in Mitchell, that inquiry focuses on the facts of the crime, not the characteristics of the criminal, and thus fits squarely within the “simple principle” analysis. 84 Or App at 458. A reasonably competent defense attorney would *162have been able to locate Mitchell’s precedent and evaluate its application to petitioner’s case with relative ease.
Moreover, because sentencing under the Act involved the possibility that petitioner would receive a more severe sentence, petitioner’s trial counsel should have explored related legal arguments to protect petitioner from such a result. Additionally, because the inquiry at issue here involved petitioner’s constitutional right to a jury trial, id,., his trial counsel was obligated reasonably to protect that right. In sum, petitioner’s trial counsel had good reason to prepare himself on the law with respect to sentencing inquiries and had access to relatively straightforward precedent. Trial counsel’s failure in that regard was constitutionally inadequate representation. See Krummacher, 290 Or at 875 (“[CJounsel must * * * prepare himself on the law * * * so that he is equipped to * * * represent the defendant in an informed manner.”).
Notwithstanding, respondent argues that, because “at the time petitioner was sentenced, no appellate court had [applied that principle to the Act,] * * * trial counsel reasonably decided * * * not to object to the * * * sentence on th[at] basis.” Respondent relies on Wells v. Peterson, 315 Or 233, 844 P2d 192 (1992), for that proposition.
In Wells, the Supreme Court held that trial counsel’s failure to challenge a sentence on the ground that it violated a statute “was not inadequate assistance of counsel because, at the time of trial, the meaning of the statute was not clearly settled.” Id. at 236. Wells does not aid respondent here, however, because the sentencing question there had been discussed by this court “with varying results[.]” Id. In other words, although examined, it was an unsettled question. Here, in contrast, the “simple principle” analysis, establishing the right to have a jury decide the elements of a crime, was well settled and its application to the Act, although untested, was analytically straightforward. Because the argument was available and apparent at the time of petitioner’s trial, an effective defense attorney at least would have raised the issue in the trial court and preserved it for appeal.4
*163Additionally, respondent argues that, “because this is an inadequate assistance claim, petitioner must show that he was prejudiced.” Respondent is correct that, “[t]o prove inadequate assistance of trial counsel, the petitioner must prove that counsel failed to do the things reasonable necessary to advance the defense and that the petitioner suffered prejudice as a result.” Davis v. Armenakis, 151 Or App 66, 69, 948 P2d 327 (1997), rev den 328 Or 83 (1998) (emphasis added). Respondent argues that petitioner here failed to establish prejudice because he failed to show that a jury would have reached a different conclusion than did the court.
However, establishing prejudice in this instance is not dependent on what the jury might have decided. Under the circumstances of this case, the issue would not be before the jury. The requirements in the dangerous offender statute — that the conduct “seriously endangered the life or safety of another — are enhancement factors, not elements of the offense of assault in the second degree, for which petitioner was convicted. However, the state did not separately plead those factors, and, accordingly, petitioner was not given notice that he would have to defend against them. Because the state failed to give petitioner the required notice that he was charged with being a dangerous offender, the jury could not have found that he was. Petitioner demonstrated prejudice here by the imposition of a 30-year sentence when the state did not plead or prove the elements necessary for that sentence.
*164Reversed with instructions to vacate petitioner’s sentence and to remand for resentencing; otherwise affirmed.
Petitioner made five other assignments of error, which we reject without discussion.
At trial, petitioner was represented by two attorneys. In this opinion, we refer to one trial counsel for purposes of simplicity.
In Mitchell, which was not decided until approximately one month after petitioner’s sentencing, we stated:
“The initial predicate for the court to invoke the dangerous offender statute and proceed to determine if a defendant is in fact a dangerous offender is the type of crime for which the defendant is being sentenced. It must be either a Class A felony or any lesser felony ‘that seriously endangered the life or safety of another.’ ORS 161.725(2). The sentencing court can determine as a matter of law whether the crime for which defendant has been convicted is a felony and whether it is a Class A or lesser felony. However, it cannot determine as a matter of law whether the felonious act seriously endangered another.
‘TA defendant! is entitled under the [Oregon! constitution to a jury determination of that factual element.” Id. at 456-57 (emphasis added).
The dissent’s basic premise is that our holding “requires trial counsel to do the job of an appellate court.” 159 Or App at 164 (emphasis in original). With *163respect, that premise misses the point entirely. We are requiring only that trial counsel do his or her job — trial advocacy. That obligation does not, as suggested by the dissent, impose on trial counsel the additional duty to predict accurately an appellate court’s response to trial counsel’s arguments. What an appellate court might do does not necessarily dictate trial counsel’s duty; what an appellate court has done, however, is absolutely germane to trial counsel’s job. Stripped to its essentials, the dissent equates constitutionally adequate representation with advocacy that is blind to fundamental and straightforward legal arguments.
The dissent’s reliance on State v. Hoffman, 236 Or 98, 385 P2d 741 (1963), further confuses its point. There, the Supreme Court held that, with respect to a court determining whether to enhance a defendant’s penalty based on evidence of prior crimes, no right to a jury trial attended because evidence of prior crimes had nothing to do with establishing the facts of the predicate offense. Id. at 107. Why that holding, which is totally consistent with Quinn and Wedge, would confuse trial counsel here about applicability of the “simple principle” is difficult to understand.