In this appeal, we are confronted with the difficult task of determining the federal constitutional consequence, if any, of two decisions by the Supreme Court of Ohio. One of these decisions for the first time construed, an Ohio statute to place the burden on the state in criminal cases of proving the absence of affirmative defenses, and the other decision held that only those defendants who had objected at the trial to jury instructions placing the burden on defendant to prove an affirmative defense could avail themselves on appeal of this interpretation of the statute.
I
Prior to 1974, Ohio followed the traditional common law rule that the defendant in a criminal ease not only had the burden of going forward with evidence to create an issue as to an affirmative defense but also had the ultimate burden of proving such affirmative defense by a preponderance of the evidence. State v. Seliskar, 35 Ohio St.2d 95, 298 N.E.2d 582 (1973). As of January 1, 1974, however, a new statutory provision became effective. That provision, codified as Ohio Revised Code § 2901.05(A), stated:
(A) Every person accused of an offense is presumed innocent until proven guilty beyond a reasonable doubt, and the burden of proof is upon the prosecution. The burden of going forward with the evidence of an affirmative defense is upon the accused.
The language of the new statute was not free of ambiguity. As a result § 2901.05(A) was not initially considered to effect any change in the previous common law rule. As late as 1975, the Supreme Court of Ohio reaffirmed at least in a dictum the principle that a defendant must bear the burden of proving affirmative defenses by a preponderance of the evidence. State v. Rogers, 43 Ohio St.2d 28, 330 N.E.2d 674 (1975).1
*1132II
In 1975, appellant, Lincoln Isaac, was indicted in Ohio for felonious assault. At his trial, Isaac asserted that he had acted in self-defense. The trial court instructed the jury without any objection by Isaac that it was incumbent on Isaac to demonstrate self-defense by a preponderance of the evidence. The jury found Isaac guilty of the lesser included offense of aggravated assault. Isaac was sentenced to a term of six months to five years imprisonment.
Prior to any appeal by Isaac, the Supreme Court of Ohio, in State v. Robinson, 47 Ohio St.2d 103, 351 N.E. 103 (1976), concluded that § 2901.05(A) had changed the previously accepted common law rule allocating the burden of proof in criminal cases. The court construed § 2901.05(A), effective January 1, 1974, to adopt the majority rule that a defendant only has the burden of coming forward with sufficient evidence to create an issue as to an affirmative defense and that once such evidence is presented, the prosecution then must demonstrate beyond a reasonable doubt the guilt of the defendant even to the extent of disproving such affirmative defense. Interpreting § 2901.-05(A) in this manner, the Supreme Court of Ohio held that any jury instruction placing the burden of proving an affirmative defense on the defendant constituted prejudicial error.
Relying on Robinson, Isaac appealed his conviction. The Court of Appeals for Pick-away County held that Isaac had waived any error in the jury instruction on burden of proof by failing to object to that instruction. Accordingly, it affirmed Isaac’s conviction. Isaac thereafter filed an appeal in the Supreme Court of Ohio. That appeal was dismissed in 1977 for lack of a substantial constitutional question.
On the same day that it dismissed Isaac’s appeal, the Supreme Court of Ohio reaffirmed the interpretation of § 2901.05(A), placing the burden on the state to prove absence of affirmative defenses, that it had made in Robinson. State v. Humphries, 51 Ohio St.2d 95, 364 N.E.2d 1354 (1977). At the same time, however, the court held that appellant Humphries could not avail himself of this interpretation of the statute because he had not objected to the charge to the jury on this ground, relying on Ohio Criminal Rule 30. The court, nevertheless, in the same opinion, held that appellant Meyer, who had had a bench trial, could effectively raise the question on appeal since Criminal Rule 30 did not apply to such trials. Ohio has continued to so apply its contemporaneous objection rule. State v. Long, 53 Ohio St.2d 91, 372 N.E.2d 804 (1978).
In 1978, Isaac sought habeas corpus relief in federal district court. Without reaching the merits of Isaac’s claim, the district court dismissed his petition. The court, relying on Wainwright v. Sykes, 433 U.S. 72, 97 S.Ct. 2497, 53 L.Ed.2d 594 (1977), held that federal habeas corpus review was precluded by an adequate state procedural ground, specifically, the Ohio rule that the failure to object to a jury instruction waived any error in such instruction.
In Isaac v. Engle, 646 F.2d 1122 (decided February 8, 1980) a panel of this court reversed the decision of the district court, Judge Celebrezze writing a concurring opinion. The focus of the panel opinion was on the constitutionality of Ohio’s use of its contemporaneous objection rule as a means of limiting the benefits of the Robinson decision. The panel opinion concluded, preliminarily, that Wainwright v. Sykes was simply not applicable and therefore there was no bar to consideration of this constitutional claim since such claim was not directed at the substantive validity of the jury instructions allocating the burden of proof. As to the merits of the claim, all three members of the panel determined that Ohio’s failure to grant Isaac the benefits of Robinson represented a denial of due process. The panel divided, however, as to the appropriate basis for reaching such a conclusion. Judges Peck and Phillips determined that Ohio’s use of its contemporaneous objection rule was arbitrary and capricious and therefore a denial of federal due process under the circumstances of this case because there was no basis for objection to *1133the jury instruction at the time of Isaac’s trial. Judge Celebrezze, adopting a somewhat broader approach, maintained that the placing of the burden of proof is so critical in the truth-finding process that the change in interpretation of the law allocating that burden must have “retroactive application” without any limitations based on state procedural rules.
We granted a petition for rehearing en banc to consider the important issues presented by this case.
Ill
We recognize that the use of a contemporaneous objection rule as a procedural device to deny a defendant the retroactive benefits of an important change in state law is arguably arbitrary and capricious when there did not exist a reasonable basis for an objection at the time of the trial. The Supreme Court, however, has at least suggested that such a use of a procedural rule may be a valid means of limiting the retroactive benefit of a new constitutional principle. Hankerson v. North Carolina, 432 U.S. 233, 244 n.8, 97 S.Ct. 2339, 2345 n.8, 53 L.Ed.2d 306 (1977). Moreover, as a matter of comity, states are entitled to some deference in the manner that they apply their own procedural rules. We are therefore hesitant to hold, as did the panel opinion, that this use of a contemporaneous objection rule to limit the retroactive benefits of a new statutory interpretation is, ipso facto, violative of due process.
We believe that the more appropriate focus is on the underlying claim, in this case the constitutional validity of the jury instructions given at Isaac’s trial as considered in light of Robinson and Humphries. In this context, the threshold question, then, is not whether the state’s limiting of the retroactive benefits of a new statutory interpretation through the use of a procedural rule is constitutional but whether that state procedural rule effectively precludes federal habeas corpus review of the underlying constitutional claim.
IV
In Wainwright v. Sykes, 433 U.S. 72, 97 S.Ct. 2497, 53 L.Ed.2d 594 (1977), the Supreme Court held that a petitioner’s failure to comply with a state procedural rule represents an independent and adequate state ground barring habeas corpus review of a constitutional claim absent a showing of cause for the noncompliance and a showing of prejudice resulting from the constitutional violation.2 The Court, however, declined to define precisely what would constitute “cause” and “prejudice.” That task was left for development in subsequent cases. While the “cause” and “prejudice” standards of Wainwright still remain somewhat undefined, we conclude that the circumstances of this case satisfy both of those standards.
At the time of Isaac’s trial, there was no indication that the jury instruction given by the trial court was contrary to state law. Ohio had traditionally placed the burden of proving affirmative defenses on the defendant. Moreover, the Supreme Court of Ohio had in a dictum stated that the recently enacted statute, Ohio Revised Code § 2901.05(A), did not change the previous common law rule. See State v. Rogers, supra. Confronted with such well-established law, it would have seemed futile for Isaac to object to a jury instruction allocating to the defendant the burden of proving self-defense. A defendant cannot be expected to predict a change in the interpretation of state law when the law is so well-established and there has been no hint of a change in that law. See O’Connor v. Ohio, 385 U.S. 92, 87 S.Ct. 252, 17 L.Ed.2d 189 (1966). Moreover, it was not, as will be seen hereafter in dealing with the merits of Isaac’s constitutional claim, until the later decision of the Supreme Court of Ohio in Robinson, supra, interpreting Ohio Revised Code § 2901.05(A) as placing the burden on the state to prove the absence of affirmative defenses, could Isaac know that the charge to the jury violated federal due process. Therefore, Isaac had legitimate *1134cause for his failure to object to the jury instruction allocating the burden of proof.
The resulting prejudice is clear. The burden of proof is a critical element of the fact-finding process in a criminal trial. See In re Winship, 397 U.S. 358, 90 S.Ct. 1068, 25 L.Ed.2d 368 (1970). An error in the allocation of that burden, here shifting from the state its burden of proving absence of self-defense beyond a reasonable doubt to the defendant to prove self-defense by a preponderance of the evidence, profoundly affects the basic fairness of a defendant’s trial. In such cases, prejudice may be presumed. Rachel v. Bordenkircher, 590 F.2d 200 (6th Cir. 1978).3
Having found both “cause” and “prejudice,” we are not precluded under Wainwright v. Sykes, supra, from considering whether it was a denial of due process to place on Isaac the burden of proving that he had acted in self-defense.
V
In In re Winship, 397 U.S. 358, 364, 90 S.Ct. 1068, 1072, 25 L.Ed.2d 368 (1970), the Supreme Court held that due process requires that the prosecution prove beyond a reasonable doubt “every fact necessary to constitute the crime.” The underlying principle of Winship is clear. A heavy burden of proof must be imposed in criminal cases in order to minimize the chances of innocent persons being convicted. But while its principle is clear, the application of Winship has proved somewhat difficult in determining to what extent the prosecution must prove the absence of any affirmative defenses raised by a defendant.
In Mullaney v. Wilbur, 421 U.S. 684, 95 S.Ct. 1881, 44 L.Ed.2d 508 (1975), the Supreme Court held unconstitutional a Maine law placing on the defendant the burden of proving that, in killing a person, he had acted in the heat of passion. The Court seemed to suggest that a state could not, consistent with due process, shift to the defendant the burden of demonstrating any fact which decreased the degree of culpability. Under this interpretation of Mullaney, the prosecution would be required to prove beyond a reasonable doubt the absence of any affirmative defense raised by the defendant, regardless of whether that affirmative defense negated an element of the crime as defined by state law.
Such a broad interpretation of Mullaney was rejected in Patterson v. New York, 432 U.S. 197, 97 S.Ct. 2319, 53 L.Ed.2d 281 (1977). In that decision, the Court upheld the validity of a New York statute allocating to the defendant the burden of proving that he had killed a person while he was under the influence of extreme emotional distress, saying:
We thus decline to adopt as a constitutional imperative, operative countrywide, that a State must disprove beyond a reasonable doubt every fact constituting any and all affirmative defenses related to the culpability of an accused. Traditionally, due process has required that only the most basic procedural safeguards be observed; more subtle balancing of society’s interests against those of the accused have been left to the legislative branch. We therefore will not disturb the balance struck in previous cases holding that the Due Process Clause requires the prosecution to prove beyond a reasonable doubt all of the elements included in the definition of the offense of which the defendant is charged. Proof of the nonexistence of all affirmative defenses has never been constitutionally required; and we perceive no reason to fashion such a rule in this case and apply it to the statutory defense at issue here.
Id. at 210, 97 S.Ct. at 2327.
We construe Mullaney and Patterson together to hold that due process requires that a state prove all elements of the crime as the state has defined the crime, that there are due process limits on the extent to which a state may shift the bur*1135den to defendant by the way in which it defines crimes, but that a state may, consistent with due process, place the burden on defendants to prove defenses that have traditionally been treated as affirmative defenses if such defense does not negate an element of the crime. Krzeminski v. Perini, 614 F.2d 121 (6th Cir. 1980).
VI
The indictment charged Isaac with felonious assault under Ohio Revised Code § 2903.11. This crime is defined by the statute as follows:
Felonious assault
(A) No person shall knowingly:
(1) Cause serious physical harm to another
However, Isaac was convicted of the lesser included offense of aggravated assault under Ohio Revised Code § 2903.12. This crime is defined by the statute as follows:
Aggravated assault
(A) No person, while under extreme emotional stress brought on by serious provocation reasonably sufficient to incite him into using deadly force, shall knowingly:
(1) Cause serious physical harm to another
At trial it was Isaac’s contention that he was not guilty of any crime because he had acted in self-defense. In this connection the trial court charged the jury, stated succinctly, that, in order to establish this defense, it was necessary that he show by the preponderance of the evidence that, in striking the other party, Isaac reasonably believed that such action was necessary to protect himself from great bodily harm.
The defense of self-defense as defined in the charge to the jury at Isaac’s trial does not negate an element of the crime of felonious assault or aggravated assault as such are defined in Ohio Revised Code § 2903.11 and § 2903.12. This is true since one could act knowingly (felonious assault) or knowingly and while under extreme emotional distress brought on by serious provocation reasonably sufficient to incite him into using deadly force (aggravated assault), and yet act in self-defense. Moreover, while according to Mullaney and Patterson, as we have noted, there are due process limits to the extent to which a state may redefine the elements of a crime and thereby reallocate the burden of proof to the defendant, Patterson holds that in failing to make absence of self-defense an element of the crimes of felonious or aggravated assault as defined in § 2903.11 and § 2903.12, Ohio did not violate due process.
Although the statutes defining felonious and aggravated assault did not make absence of self-defense an element of the crime, it is arguable that, in enacting the statute that was construed to place the burden on the state of proving absence of self-defense, Ohio had so made it an element of the crime. In State v. Humphries, supra, 51 Ohio St.2d at 111, 364 N.E.2d 1354, one of the Ohio justices did say that, in so construing Ohio Revised Code § 2901.-05(A), absence of affirmative defenses had been made an element of the crimes. (Locher, J., concurring in part and dissenting in part). We believe, however, that, under Mullaney and Patterson, the proper question to ask is: Can Ohio, having by statute assumed the burden of proof with respect to absence of self-defense, consistently with due process convict a defendant by applying a different and lesser standard of proof.
As we read Mullaney and Patterson, while the states are largely free to define crimes as they choose, fundamental fairness and therefore due process require that they prove the elements of the crimes, as the states have chosen to define them, beyond a reasonable doubt. We further conclude that, once a state assumes the burden of proving the absence of an affirmative defense beyond a reasonable doubt, fundamental fairness and therefore due process require it to meet the burden that it chose to assume. From the point of view of fairness and due process, there is no practical difference between requiring a state to prove the elements of crimes beyond a reasonable doubt and requiring it to meet its *1136assumed burden of proving absence of affirmative defenses beyond a reasonable doubt. Thus we conclude that, in Isaac’s trial, placing the burden on him to prove self-defense by a preponderance of the evidence constituted a denial of federal due process.
VII
Following the decisions of the Supreme Court of Ohio in Robinson and Humphries, the Ohio legislature amended Ohio Revised Code § 2901.05(A) so as to readopt the common law rule that a defendant must prove any affirmative defense by a preponderance of the evidence. On any retrial, Isaac is entitled to jury instructions consistent with Ohio law in 1975 as construed in Robinson. Any other result would give ex post facto effect to the 1978 amendment of § 2901.05(A). See Breest v. Helgemoe, 579 F.2d 95 (1st Cir.), cert. denied, 439 U.S. 933, 99 S.Ct. 327, 58 L.Ed.2d 329 (1978); United States v. Williams, 475 F.2d 355 (D.C.Cir. 1973).
Accordingly, the judgment of the district court is reversed and the case is remanded. The district court is directed to order that Isaac be released from custody unless Ohio chooses to retry him within a reasonable time to be determined by the district court.
. In Rogers, the Ohio Supreme Court stated: The defense of using reasonable force to effect a citizen arrest necessarily involves an allegation of excuse or justification, and is, therefore, an affirmative defense (R.C. 2901.-05[C][2]> which places the burden of going forward with the evidence upon the accused (R.C. 2901.05[A]) to prove that issue by a preponderance of the evidence. See State v. Seliskar, supra, 35 Ohio St.2d 95, 298 N.E.2d 582.
. See also Hockenbury v. Sowders, 620 F.2d 111 (6th Cir. 1980).
. Since at trial Isaac by his testimony made a substantial issue as to his self-defense contention, he was in fact prejudiced by the court’s charge to the jury and therefore Isaac need not rely on such presumption.