OPINION
CLAY, Circuit Judge.
Defendant, Michael D. Stubbs, appeals from his judgment of conviction and sentence after pleading guilty to three counts of a thirteen-count indictment. One of the counts to which Defendant pleaded guilty charged that he had conspired to use or possess firearms during and in relation to the commission of a drug trafficking crime in violation of 21 U.S.C. § 846 and 18 U.S.C. § 924(o). For this count, Defendant was sentenced under 18 U.S.C. § 924(c) to a mandatory 60-month term of imprisonment to be served consecutive to all other sentences. On appeal, Defendant argues that the district court erred in sentencing him under 18 U.S.C. § 924(c) when he in fact was charged with and pleaded guilty to a violation 18 U.S.C. § 924(o), which carries a term of imprisonment of up to 20 years. For the reasons that follow, we VACATE Defendant’s sentence and REMAND for resentencing.
BACKGROUND
On September 17, 1997, a Northern District of Ohio grand jury returned a thirteen-count indictment charging Defendant in three of the thirteen counts. Defendant was charged (1) in count one with conspiracy to distribute and possess with the intent to distribute cocaine, cocaine base and marijuana, in violation of 21 U.S.C. § 841(a)(1) and 21 U.S.C. § 846; (2) in count twelve with aiding and abetting two co-defendants with traveling in interstate commerce with the intent to murder in violation of 18 U.S.C. §§ 2, 1958; and (3) in count thirteen with conspiracy to use and carry firearms during and in relation to the commission of a drug trafficking crime in violation of 21 U.S.C. § 846 and 18 U.S.C. § 924(o).
Defendant’s trial counsel and the government negotiated a plea agreement during jury selection. Pursuant to that written plea agreement, Defendant pleaded guilty to all three counts of the indictment in which he was charged. The plea agreement provided that count thirteen, which charged Defendant with violating § 924(o), called for a mandatory consecutive term of 60 months’ imprisonment. The plea agreement also provided that Defendant waived his right to directly appeal his sentence or seek post-conviction relief such as that offered under 28 U.S.C. § 2255. The agreement provided that Defendant only preserved the right to appeal “(a) any punishment imposed in excess of a statutory maximum, or the terms stated within this agreement; and (b) any punishment to the extent it constitutes an upward departure from the guidelines range deemed most applicable by the sentencing court; and (c) any other issue directly relating to [406]*406the interpretation, application, or enforcement of this agreement.” (J.A. at 52.)
On April 28, 1998, the district court held a plea hearing and accepted Defendant’s guilty plea. The district court found that there was a factual basis for the plea agreement, that Defendant was competent to make the plea agreement, and that Defendant’s guilty plea in accordance with the plea agreement was knowing and voluntary.
Defendant filed a pro se motion to withdraw his guilty plea on October 6, 1998. Defendant argued that he had received ineffective assistance of counsel, that the Pre-Sentence Investigation Report was not in accordance with the plea agreement, and that his plea agreement was not knowing and voluntary because he was coerced into the agreement without time or information to make a wise decision. The district court denied the motion to withdraw after a hearing on March 12,1999.
Defendant appeared for sentencing on May 10, 1999 where the district court sentenced Defendant to 135 months of imprisonment for counts one and twelve to be served concurrently, and to 60 months of imprisonment for count thirteen to be served consecutive to the 135-month sentence. Defendant was also sentenced to 5 years of supervised release and ordered to pay a special assessment of $300.
This timely appeal followed.
ANALYSIS
Defendant now appeals his sentence for a violation of § 924(o) arguing that the district court erred in sentencing him to a mandatory 60-month consecutive sentence under § 924(c). Defendant argues that he could not be sentenced under § 924(c) when he was only charged with and he only pleaded guilty to a violation of § 924(o).
The government argues, however, that Defendant’s sentence is proper under the sentencing guidelines. Specifically, the government argues that USSG § 2K2.1(c) applies to Defendant’s offense. Section 2K2.1(c) provides in pertinent part:
(a) If the defendant used or possessed any firearm or ammunition in connection with the commission or attempted commission of another offense, or possessed or transferred a firearm or ammunition with knowledge or intent that it would be used or possessed in connection with another offense, apply—
(A) § 2X1.1 (Attempt, Solicitation, or Conspiracy) in respect to that other offense, if the resulting offense level is greater than that determined above ...
USSG § 2K2.1(c)(l)(A) (1998). Section 2X1.1 in turn provides that when sentencing for an offense involving attempt, solicitation or conspiracy, the court is to use the base offense level from the guideline for the substantive offense. USSG § 2X1.1 (1998). The government argues that the substantive offense in this case is a violation of § 924(c), which is covered by USSG § 2K2.4. Section 2K2.4 provides that the term of imprisonment for offenses under § 924(c) is that required by statute, which is a mandatory consecutive, minimum 60-month sentence. USSG § 2K2.4. The government therefore argues that under the cross-reference provisions in the guidelines, Defendant’s sentence is proper.
Defendant counters that § 2K2.1(c) does not apply to his case. Instead, Defendant argues, § 2K2.1(a), (b) govern the calculation of his offense level and thus his sentencing range under the sentencing guidelines.
We agree with Defendant that he was improperly sentenced under § 924(c) when he was charged with and pleaded guilty to [407]*407a violation of § 924(o). We reject the government’s contention that Defendant’s sentence is proper under USSG § 2K2.1(c); and we hold that Defendant’s challenge to his sentence is not barred by his written waiver of his right to appeal inasmuch as Defendant’s plea agreement, and thus the waiver, was not knowing and voluntary.
I.
Because Defendant did not object to his sentence on the ground now alleged, our review is limited to plain error. United States v. Koeberlein, 161 F.3d 946, 949 (6th Cir.1998). Under plain error review, this Court may only reverse if (1) there is error; (2) the error is plain; (8) the error affects the defendant’s substantial rights; and (4) the fairness, integrity or public reputation of the judicial process is seriously affected. Id. We conclude that reversal is proper in the instant case because there was plain error that affected Defendant’s substantial rights, which seriously affects the fairness, integrity or public reputation of the judicial process.
We begin with the rudimentary principle that, except in narrow circumstances not relevant here, an indictment is a necessary prerequisite to a conviction and sentence when a defendant is charged with a felony offense in federal court. Stirone v. United States, 361 U.S. 212, 217, 80 S.Ct. 270, 4 L.Ed.2d 252 (1960). An indictment is sufficient if it charges an offense, contains the elements of that offense, and fairly informs the defendant of the charge against him. Hamling v. United States, 418 U.S. 87, 117, 94 S.Ct. 2887, 41 L.Ed.2d 590 (1974); accord Jones v. United States, 526 U.S. 227, 119 S.Ct. 1215, 143 L.Ed.2d 311 (1999). Furthermore, it is well-established that after an indictment has been returned, its charge may not be broadened except by amendment by the grand jury itself. Stirone, 361 U.S. at 217-18, 80 S.Ct. 270; see also United States v. Miller, 471 U.S. 130, 138, 105 S.Ct. 1811, 85 L.Ed.2d 99 (1985) (citing Stirone, 361 U.S. at 217-18, 80 S.Ct. 270).
We find the Supreme Court’s decision in Jones instructive in resolving the case at bar. There, the Supreme Court held that elements of an offense must be charged in the indictment, submitted to a jury and proven beyond a reasonable doubt. 526 U.S. at 232, 119 S.Ct. 1215. In Jones, the defendant was indicted under 18 U.S.C. § 2119, but the indictment did not specify a particular subsection under § 2119. At trial, the defendant was convicted under jury instructions corresponding to subsection (1) which carried a maximum penalty of fifteen years. Id. at 230-31, 119 S.Ct. 1215. The presentence report, however, recommended that the defendant be sentenced to twenty-five years because one of the victims suffered serious bodily injury, referencing subsection (2) and testimony from the trial. Id. at 231, 119 S.Ct. 1215. The district court adopted the recommendation of the presentence report, finding that the serious bodily injury had been proven by a preponderance of the evidence. Id.
The government argued before the Supreme Court that the sentence should stand because the subsections of § 2119 were only sentencing factors and therefore did not have to be pleaded in the indictment, submitted to a jury, and proven beyond a reasonable doubt. The Court rejected this argument, finding that “the Government’s view would raise serious constitutional questions.” Jones, 526 U.S. at 251, 119 S.Ct. 1215. The Court concluded that because each subsection of § 2119 called for a different range of statutory penalties, each subsection constituted a different offense. Therefore, due process and the Sixth Amendment required that each element be charged in the indictment, [408]*408submitted to a jury, and proven beyond a reasonable doubt. Id. at 244-52, 119 S.Ct. 1215.
Prior to Jones, however, the First Circuit concluded that, in some instances, use of § 2K2.1(c) created a due process problem. See United States v. Lombard, 72 F.3d 170 (1995).1 In Lombard, the defendant was charged with and convicted of unlawful possession of a firearm in violation of 18 U.S.C. §§ 922(g), 924(e). Because the defendant’s primary offense, a violation of § 922(g), involved a firearm, § 2K2.1 applied in his case. There, the district court applied subsection (c), which provided for the cross-reference. The district court considered a murder, of which the defendant was acquitted in state court and was not charged in federal court, as “another offense”. The district court concluded, by a preponderance of the evidence that the defendant had committed the offenses and applied § 2X1.1, which directed the court to the base offense level for the underlying offense, which was first-degree murder. Consequently, the defendant was subject to a mandatory life sentence. Id. at 175.
On appeal, the First Circuit vacated the sentence and remanded the case, opining that
[t]he effect here has been to permit the harshest penalty outside of capital punishment to be imposed not for conduct charged and convicted but for other conduct as to which there was, at sentencing, at best a shadow of the usual procedural protection, such as the requirement of proof beyond a reasonable doubt.... The punishment imposed in view of this other conduct far outstripped in degree and kind the punishment Lombard would otherwise have received for the offense of conviction.
72 F.3d at 177. Among other things, the court was particularly troubled that “[u]n-like certain ‘relevant conduct’ guidelines that simply call for a determinate increase in a defendant’s [base offense level] based on specified factual findings ..., the cross-reference provision that was applied in this case, U.S.S.G. § 2K2.1(c), required the district court to calculate [the defendant’s base offense level] as if his offense of conviction had been murder.” Id. (emphasis in original). While it appears that the factor that most influenced the court to vacate the sentence was the harshness of the penalty, the court nevertheless recognized that,
through the mechanisms of the Guidelines ..., the sentencing phase of the defendant’s trial produced the conclusion he had committed murder and mandated imposition of a life sentence, but without the protections which normally attend the criminal process, such as the requirement of proof beyond a reasonable doubt.
Id. at 179-80.
This Court, in United States v. Flowal, 234 F.3d 932 (6th Cir.2000) and United States v. Ramirez, 242 F.3d 348 (6th Cir.2001), concluded that Apprendi v. New Jersey, 530 U.S. 466, 120 S.Ct. 2348, 147 L.Ed.2d 435 (2000),2 applied any time a [409]*409factual determination changed the statutorily prescribed range of sentences. In Flowal, the Court held that “[b]eeause the amount of the drugs at issue determined the appropriate statutory punishment, a jury should have determined the weight of the drugs beyond a reasonable doubt.” 234 F.3d at 937. Similarly, in Ramirez, this Court stated that,
in the language of Apprendi ... “the assessment of facts that increase the prescribed range of penalties to which a criminal defendant is exposed,” such as moving up the scale of mandatory minimum sentence, invokes the full range of constitutional protections required for “elements of the crime.”
242 F.3d at 351 (citation omitted).
The case at bar is different from Jones or Apprendi in that the Defendant’s sentence was not enhanced based upon some factual finding. Indeed, we consider this case to be more fundamental because Defendant was indicted for one offense and sentenced under another simply by operation of a cross-reference in the sentencing guidelines and without many of the procedural safeguards necessary for a criminal proceeding. Although Jones, Apprendi and their progeny do not address the precise issue presented by this case, the principles espoused therein are instructive.
There can be no doubt that § 924(c) and § 924(o) charge different offenses. Each statute requires different levels of proof as to conduct and mens rea. And, most notably, these two statutory provisions call for significantly different statutory penalties, which under Jones makes them different offenses. The government must therefore charge each offense and the elements thereof in an indictment. Because the government cannot broaden the scope of the indictment without an amendment by the grand jury, Defendant cannot be sentenced under § 924(c) unless the indictment charged him with a violation of § 924(c). We therefore conclude that it was plain error for the district court to sentence Defendant under § 924(c) when he had only pleaded guilty to a violation of § 924(o) and the penalties of that statute are clear on its face.
We reject the government’s contention that Defendant’s sentence is proper under USSG § 2K2.1(c). Foremost, the government cannot evade the constitutional requirements of the Sixth Amendment and due process by application of the sentencing guidelines. Application of the cross-reference provision as the government suggests leads to a change in both the crime of conviction and the statutory sentencing range. This result runs contrary to fundamental principles of due process, the Sixth Amendment right to notice through indictment by a grand jury, and this Court’s decisions in Ramirez and Flo-wal.
The government’s argument must also fail because its interpretation of USSG § 2K2.1(c) does not comport with the clear and plain language of the guideline. By its own terms, § 2K2.1(c) applies if the defendant uses or possesses the firearm in connection with “another” offense, i.e., an offense other than the firearm offense for which the guideline is being applied in the first instance. There is no basis for concluding that the very firearm offense that triggers the application of § 2K2.1 also constitutes “another” offense as referenced in subsection (c). If the triggering offense and the offense referenced in subsection (c) could be the same offense, there would be no need to use the word “another”. Furthermore, it is a fore[410]*410gone conclusion that a defendant will either use or possess (actual or constructive) a firearm in connection with most firearm offenses such that subsection (c) could, and would likely, apply to any offense under § 2K2.1. This interpretation would make the other provisions of § 2K2.1 virtually superfluous. Therefore, constitutional infirmities aside, we reject the government’s contention that § 2K2.1 applies to Defendant’s case in the first instance.
We also conclude that Defendant’s substantial rights were affected by the district court’s error. An error affects the defendant’s substantial rights if it prejudices the defendant, i.e., if it affects the outcome of the district court’s proceedings. United States v. Page, 232 F.3d 536, 544 (6th Cir.2000). Because of the erroneous application of § 924(c), the district court had no choice but to sentence Defendant to a mandatory consecutive 60 month sentence. If Defendant had been properly sentenced under § 924(o), he would not have been subject to a mandatory minimum sentence and there would not have been a requirement that the sentence be served consecutive to any other sentenced imposed. The erroneous application of § 924(c) therefore affected the outcome of the district court’s proceedings establishing that Defendant’s substantial rights were affected, i.e., that he was prejudiced by the error.3
There is no question that our criminal justice system is sorely lacking in the procedural safeguards mandated by the Constitution when a defendant can be charged with one crime and sentenced for another. Inasmuch as an error of this magnitude, an error which runs contrary to the administration of justice and the fundamental constitutional principles of due process and the Sixth Amendment right to notice, substantially and adversely affects the integrity of the judicial process, we are compelled to correct it.
II.
We also reject the government’s argument that Defendant cannot appeal the erroneous sentence imposed by the district court because he waived his right to appeal his sentence. It is true that under his plea agreement, Defendant waived the right to appeal his sentence except where the punishment imposed exceeded the statutory maximum or the terms of the agreement, or where the punishment constituted an upward departure from the guideline range deemed most applicable by the sentencing court. Defendant could also appeal any other issue directly related to the interpretation, application and enforcement of the plea agreement.
Certainly, when a Defendant waives his right to appeal his sentence in a valid plea agreement, this Court is bound by that agreement and will not review the sentence except in limited circumstances. Hunter v. United States, 160 F.3d 1109, 1113 (6th Cir.1998); Everard v. United States, 102 F.3d 763, 766 (6th Cir.1996). However, this is based upon the notion that the plea agreement itself is constitutionally valid, i.e, it is knowing and voluntary. Defendant argues on appeal that his waiver is not valid because his plea was not knowing and voluntary and because he received ineffective assistance of counsel. Because we agree that Defendant’s guilty plea was not knowing and voluntary, we [411]*411decline to address whether Defendant received ineffective assistance of counsel.4
Whether Defendant entered into a valid plea agreement and thus waived his right to appeal his sentence is a question of law subject to de novo review. See United States v. Walker, 160 F.3d 1078, 1096 (6th Cir.1998).
“ ‘[I]f a defendant’s guilty plea is not ... voluntary and knowing, it has been obtained in violation of due process and is therefore void. Moreover, because a guilty plea is an admission of all the elements of a formal. criminal charge, it cannot be truly voluntary unless the defendant possesses an understanding of the law in relation to the facts.’ ” Boykin v. Alabama, 395 U.S. 238, 243 n. 5, 89 S.Ct. 1709, 23 L.Ed.2d 274 (1969) (quoting McCarthy v. United States, 394 U.S. 459, 466, 89 S.Ct. 1166, 22 L.Ed.2d 418 (1969)). This Court has held that a guilty plea “is not deemed voluntary where the person entering it does so without understanding of the consequences of his plea.” Smith v. United States, 400 F.2d 860, 862 (6th Cir.1968) (per curiam) (holding that the guilty plea was not voluntary where the defendant was under mistaken belief that the sentence for the crime to which he pleaded guilty could be served concurrently with the sentence he was already serving, and his mistaken belief was not corrected by his attorney or the district court).
In Pitts v. United States, 763 F.2d 197 (6th Cir.1985), the defendant alleged that his guilty plea was not knowing and voluntary because he was incorrectly informed of the consequences of his guilty plea. The district court had informed the defendant that he could receive up to twenty-five years of imprisonment and a $25,000 fine; however, under the applicable statutes, the defendant could only receive up to fifteen years of imprisonment and a $20,000 fine. Id. at 199. In concluding that the district court erred in denying the defendant habeas relief on the ground that his guilty plea was involuntary, this Court stated,
[w]e stress that this case does not involve a mere failure to give a defendant some information for which he later claims would have affected his pleading decision. Instead it involves affirmative misstatements of the maximum possible sentence. Numerous cases have held that misunderstandings of this nature invalidate a guilty plea.
Id. at 201. The Court continued,
[although the government argues that the presence of the plea agreement in this case renders this misadvice [regarding the maximum possible sentence] insignificant, the effect of the plea agreement may have been to exacerbate the problem. When considering a plea agreement, a defendant might well weigh the terms of the agreement against the maximum sentence he could receive if he went to trial. When the maximum possible sentence exposure is overstated, the defendant might well be influenced to accept a plea agreement he would otherwise reject.
Id.; see also United States v. Goins, 51 F.3d 400, (4th Cir.1995) (holding that district court’s failure to inform defendant of mandatory minimum sentence that would be imposed as a result of guilty plea constituted reversible error where defendant was in fact subject to mandatory minimum sentence and there was no evidence that [412]*412defendant was aware of mandatory minimum sentence).
A similar conclusion was reached in Bousley v. United States, 523 U.S. 614, 118 S.Ct. 1604, 140 L.Ed.2d 828 (1998). There, the defendant argued on habeas review that his guilty plea was unintelligent because the district court misinformed him as to the elements of a § 924(c)(1) offense, the crime to which he pleaded guilty. Id. at 618, 118 S.Ct. 1604. The defendant in Bousley had been sentenced prior to the Supreme Court’s decision in Bailey v. United States, 516 U.S. 137, 116 S.Ct. 501, 133 L.Ed.2d 472 (1995), which held that the “use” prong of a § 924(c)(1) violation requires that the government prove “active employment of the firearm.” See Bousley, 523 U.S. at 616, 118 S.Ct. 1604. The defendant therefore argued that under Bailey, the district court had misinformed him of the nature of the crime charged. The Bousley Court held that its decision in Bailey applied to the defendant’s case despite the fact that he had pleaded guilty prior to the Court’s decision in Bailey. Id. at 620-21, 118 S.Ct. 1604. The Court also concluded that if the essential elements of the crime with which the defendant was charged were not understood by the defendant, his counsel, or the district court, then the defendant’s guilty plea “would be ... constitutionally invalid.” Id. at 618-19, 118 S.Ct. 1604.
We similarly conclude that Defendant’s guilty plea in the case at bar is constitutionally invalid. The record reveals that neither Defendant, his counsel nor the district court was aware that Defendant was not subject to a mandatory consecutive minimum 60-month sentence under § 924(o). There is no record evidence which demonstrates that Defendant was aware of the true nature of the crime charged and the proper statutory consequences of his guilty plea.
Furthermore, it is reasonably probable that but for the misinformation as to Defendant’s proper statutory sentence, Defendant would not have pleaded guilty. See United States v. Gigot, 147 F.3d 1193, 1198-99 (10th Cir.1998) (holding that the guilty plea was not intelligent and knowing where the defendant was not advised of the elements of the crime charged and the resulting penalties). Here, Defendant was ready to proceed to trial when his counsel suggested that he plead guilty. Moreover, Defendant had moved to withdraw his guilty plea based in part on the ground that his counsel had not properly informed him of the nature of the charge against him, albeit for a different reason. It is therefore reasonably probable that had Defendant known that he was not subject to a mandatory consecutive 60-month sentence, but rather was subject to a sentence of up to twenty years that could be served concurrent to any other sentenced received, Defendant would not have pleaded guilty.
We therefore conclude that Defendant’s guilty plea was not knowing and voluntary and thus could not serve as a basis for waiver of his right to appeal his sentence.5
CONCLUSION
A defendant is entitled to withdraw his guilty plea if it is constitutionally [413]*413infirm; however, Defendant does not seek to withdraw his guilty plea in the instant case. Instead, Defendant simply seeks to be properly sentenced under § 924(o). Accordingly, we VACATE Defendant’s sentence and REMAND for resentencing in accordance with this opinion.6