TACHA, Circuit Judge.
A jury convicted defendant Luis Santiago Ramirez of possessing more than 500 grams of cocaine with intent to distribute in violation of 21 U.S.C. § 841(a)(1) and (b)(1)(B), conspiracy to possess more than 500 grams of cocaine with intent to distribute in violation of 21 U.S.C. § 846 and 21 U.S.C. § 841(a)(1) and (b)(1)(B), and carrying or using a firearm during and in relation to a drug trafficking offense in violation of 18 U.S.C. § 924(e).1 He was sentenced to a total of 123 months imprisonment and a term of supervised release. Defendant now appeals. We have jurisdiction under 28 U.S.C. § 1291, and we affirm.
I
On June 11, 1993, a confidential informant purchased cocaine from defendant at a building at 838 Bridge Southwest in Albuquerque, New Mexico (“the building”). The controlled buy was part of a narcotics investigation conducted by officers from the Sandoval County Sheriffs Office, including Lieutenant Ramiro Flores. During the buy, officers observed defendant use a key to open the building, enter alone, leave the building, and hand cocaine to a confidential informant. Officers had observed defendant entering the building on two other occasions.
Ten days later, Officer Flores and another officer approached the building with a search warrant. Carmelo Rojas, one of Ramirez’s codefendants, allowed the officers to enter. They conducted a search of the premises and found a triple-beam scale, plastic baggies, six ounces of cocaine, and a loaded revolver. Their search of Rojas uncovered $840 cash, including a $20 bill that the informant had given defendant during the controlled buy.
While the officers were still searching the premises, the telephone at the building rang. Officer Flores answered the phone, and the [940]*940caller asked in Spanish what was going on. The caller identification box indicated that the call had been placed from a pay phone at a gas station at the end of the block. Officer Flores called a nearby surveillance team, which apprehended defendant near the gas station and escorted him to the building. The officers searched defendant and found $940 cash and a key to the building on his person. The search of the building subsequently uncovered an additional kilogram of cocaine in a trash basket and three ounces of cocaine hidden in a pair of boots.
Defendant was charged with one count of possessing more than 500 grams of cocaine with intent to distribute, one count of conspiracy to do the same, and one count of using a firearm in relation to a drug trafficking offense. Defendant timely moved to suppress the evidence seized in the search of the building. The district court conducted a hearing on the matter and denied defendant’s motion. Defendant then filed a motion in limine to exclude evidence of a prior drug-related arrest. The district court denied this motion as well.
Defendant’s trial began October 4, 1993. On October 7, the jury returned a verdict of guilty on all three counts. Defendant then filed a motion to dismiss based on comments made by the prosecution during its closing argument, which the district court denied. On September 23, 1994, the court sentenced defendant to 63 months imprisonment on counts one and two, with the sentences to run concurrently, and 60 months for count three, with the sentence to run consecutively. Defendant now appeals.
II
Defendant first contends that the district court should have suppressed the evidence seized at the building pursuant to the warrant because the issuing magistrate was not neutral and detached. Judge James Blaek-mer, a New Mexico state district court judge, issued the warrant based on an application presented by Officer Flores. After reading Officer Flores’s supporting affidavit, Judge Blackmer altered the warrant and that portion of the affidavit listing the items to be searched and seized. Specifically, he (1) inserted the word “and” between “person” and “place” on the warrant, (2) added the words “and Luis Ramirez himself’ to the items to be searched on the affidavit, and (3) added the words “keys to the doors and/or locks on the doors at 838 Bridge, Southwest” to the items to be seized on the affidavit. Defendant argues that, because Judge Blackmer “substantially altered” the affidavit and the warrant, he abandoned his judicial role and was no longer neutral and detached from the investigation.2
On appeal from the denial of a motion to suppress evidence, we review the factual determinations made by the district court for clear error, and we view the evidence in the light most favorable to the government. United States v. Bell, 892 F.2d 959, 965 (10th Cir.1989), cert. denied, 496 U.S. 925, 110 S.Ct. 2618, 110 L.Ed.2d 639 (1990). A factual determination is clearly erroneous only if there is no factual support in the record or if we are “left with the definite and firm conviction that a mistake has been made.” LeMaire v. United States, 826 F.2d 949, 953 (10th Cir.1987). The ultimate question of whether a search or seizure comported with the Fourth Amendment, however, is a legal issue, which we review de novo. United States v. Lyons, 7 F.3d 973, 975 (10th Cir.1993).
In Johnson v. United States, 333 U.S. 10, 68 S.Ct. 367, 92 L.Ed. 436 (1948), Justice Jackson delivered perhaps the quintessential explication of the policies underlying the Fourth Amendment:
[941]*941The point of the Fourth Amendment, which often is not grasped by zealous officers, is not that it denies law enforcement the support of the usual inferences which reasonable men draw from evidence. Its protection consists in requiring that those inferences be drawn by a neutral and detached magistrate instead of being judged by the officer engaged in the often competitive enterprise of ferreting out crime.
Id. at 13-14, 68 S.Ct. at 369. For purposes of the Fourth Amendment, it is essential that a magistrate issuing a search warrant be neutral and detached rather than “an adjunct law enforcement officer.” United States v. Leon, 468 U.S. 897, 914, 104 S.Ct. 3405, 3416, 82 L.Ed.2d 677 (1984); Lo-Ji Sales, Inc. v. New York, 442 U.S. 319, 327, 99 S.Ct. 2319, 2324-25, 60 L.Ed.2d 920 (1979). It therefore follows that a search premised on a warrant issued by a magistrate who lacks such neutrality and detachment “stands on no firmer ground than if there had been no warrant at all.” Coolidge v. New Hampshire, 403 U.S. 443, 453, 91 S.Ct. 2022, 2031, 29 L.Ed.2d 564 (1971).
Judge Blaekmer’s alteration of the search warrant does not call into question his neutrality or detachment in this case. Indeed, as a judicial officer, it is the duty of an issuing magistrate to ensure that a warrant corresponds to the content of the supporting affidavit. Determinations concerning the content of a supporting affidavit, however, are generally the province of law enforcement officers. Thus, Judge Blaekmer’s additions to the affidavit itself are more troubling, requiring more careful analysis.
Clearly, a magistrate’s alteration of a warrant applicant’s affidavit can constitute evidence that the magistrate abandoned her judicial role. We decline, however, to adopt any per se rule requiring suppression whenever a magistrate alters an affidavit. Whether a magistrate was neutral and detached in any particular case is necessarily an individualized and contextual inquiry. Courts must focus on the specific circumstances surrounding the issuance of the warrant and decide whether the magistrate “manifest[ed] that neutrality and detachment demanded of a judicial officer when presented with a warrant application for a search and seizure.” Lo-Ji Sales, 442 U.S. at 326, 99 S.Ct. at 2324.
In this case, the district court conducted an evidentiary hearing on the matter. That hearing revealed that Judge Blaekmer read the narrative portion of Officer Flores’s affidavit and “realized that there was sufficient probable cause to believe that Luis Ramirez himself would have possession of controlled substances, cocaine and/or paraphernalia for it.” He also concluded that defendant’s key to the building “was a material piece of evidence that would be useful in a possible criminal prosecution.” Judge Blaekmer accordingly altered the affidavit so as to permit the executing officers to search defendant himself and to seize defendant’s key to the building. His additions to the affidavit were mere common sense extensions of the contents of the narrative portion of the same affidavit.
Under these circumstances, we agree with the district court that such common sense changes to the affidavit “do not indicate that Judge Blaekmer breached his duty to be a neutral and detached magistrate.” Cf. United States v. Banks, 539 F.2d 14, 16 (9th Cir.) (holding that the commanding officer of a military reservation was sufficiently neutral and detached because he had not “participated in any way in the investigation or prosecution” of the defendant), cert. denied, 429 U.S. 1024, 97 S.Ct. 644, 50 L.Ed.2d 626 (1976); United States v. Dorman, 657 F.Supp. 511, 514 (M.D.N.C.1987) (concluding that the magistrate did not abrogate her constitutional obligation to be neutral and detached even though she “summon[ed] ... a detective to assist in the investigation of a matter currently before [her]”), aff'd, 846 F.2d 74 (4th Cir.1988); United States v. Evans, 629 F.Supp. 1544, 1554 (D.Conn.1986) (holding that a magistrate who “suggested that the warrant application and warrant itself include [certain] items” was not so “involve[d] in the application for the search warrant as to disqualify [him] on grounds that he lacked the requisite neutrality”). First, the changes to the affidavit constituted rather minor additions to the list of items to be searched or seized. The Fourth Amendment does not require magistrates “to maintain Sphinx-like [942]*942inscrutability in passing on warrant applications.” United States v. Levasseur, 699 F.Supp. 965, 988 (D.Mass.), rev’d in part on other grounds, 846 F.2d 786 (1st Cir.), cert. denied, 488 U.S. 894, 109 S.Ct. 232, 102 L.Ed.2d 222 (1988). Second, each of the additions were based on Judge Blaekmer’s conclusion that the narrative portion of the affidavit provided probable cause to support the search or seizure of these items, and defendant does not challenge the search or seizure of these items on the ground that the warrant lacked probable cause. Finally, Judge Blackmer’s altering of the affidavit is a far cry from the conduct or circumstances that the Supreme Court has held to compromise a magistrate’s neutrality and detachment. Cf. Lo-Ji Sales, 442 U.S. at 327, 99 S.Ct. at 2324-25 (holding that the town justice who had issued a warrant acted as an “adjunct law enforcement officer” when he “allowed himself to become a member, if not the leader, of the search party which was essentially a police operation”); Connally v. Georgia, 429 U.S. 245, 250, 97 S.Ct. 546, 548-49, 50 L.Ed.2d 444 (1977) (per curiam) (declaring unconstitutional a Georgia system under which magistrates were paid based on the number of warrants that they issued and therefore had a direct financial interest in approving warrant applications); Coolidge, 403 U.S. at 450, 91 S.Ct. at 2031 (holding that a state attorney general, “who was actively in charge of the investigation and later was to be chief prosecutor at the trial,” was not neutral and detached for purposes of the Fourth Amendment).
We therefore find that Judge Blackmer did not abrogate his duty to be neutral and detached in passing on Officer Flores’s warrant application. The district court did not err in refusing to suppress the evidence seized pursuant to the search of the building.3
III
Defendant’s next claim concerns the trial court’s admission of evidence that defendant was previously arrested for possession with intent to distribute cocaine. At trial, the government called Albuquerque Police Officer Thomas Garduño. Garduño testified that defendant had been arrested for possession with intent to distribute cocaine on July 11, 1992. Garduño also testified that, at the time of that arrest, defendant had been found in possession of eight ounces of cocaine and roughly $43,000 in cash. The district court admitted the evidence pursuant to Fed. R.Evid. 404(b). We review a trial court’s evidentiary rulings only for an abuse of discretion. United States v. Cestnik, 36 F.3d 904, 906 (10th Cir.1994), cert. denied, — U.S. —, 115 S.Ct. 1156, 130 L.Ed.2d 1113 (1995).
Under Rule 404(b),4 evidence of a defendant’s prior crimes, wrongs, or acts is “admissible only for limited purposes and only when various prerequisites are satisfied.” United States v. Robinson, 978 F.2d 1554, 1558 (10th Cir.1992), cert. denied, — U.S. —, 113 S.Ct. 1855, 123 L.Ed.2d 478 (1993). As this court has stated on several occasions, Rule 404(b) requires that
(1) the evidence must be offered for a proper purpose; (2) the evidence must be relevant; (3) the trial court must make a Rule 403 determination of whether the probative value of the similar acts is substantially outweighed by its potential for unfair prejudice; and (4) pursuant to Fed. R.Evid. 105, the trial court shall, upon request, instruct the jury that the evidence of similar acts is to be considered only for the proper purpose for which it was admitted.
United States v. Jefferson, 925 F.2d 1242, 1258 (10th Cir.), cert. denied, 502 U.S. 884, 112 S.Ct. 238, 239, 116 L.Ed.2d 194 (1991); [943]*943see also United States v. Johnson, 42 F.3d 1312, 1315 (10th Cir.1994) (quoting the same), cert. denied, — U.S. —, 115 S.Ct. 1439, 131 L.Ed.2d 318 (1995); United States v. Poole, 929 F.2d 1476, 1481 (10th Cir.1991) (same). We address each element in turn.
First, the record reveals that the government introduced Garduno’s testimony to show defendant’s intent to possess and distribute cocaine, and that his participation in the conspiracy was knowing. This court has repeatedly held that “the use of prior drug involvement to show plan, motive or intent in a drug trafficking offense is appropriate.” United States v. Sturmoski, 971 F.2d 452, 459 (10th Cir.1992); see also United States v. Record, 873 F.2d 1363, 1375 (10th Cir.1989); United States v. Mora, 845 F.2d 233, 237 (10th Cir.), cert. denied, 488 U.S. 995, 109 S.Ct. 562, 102 L.Ed.2d 587 (1988). Indeed, Rule 404(b) expressly provides that evidence of prior crimes is admissible for “proof of ... intent, ... plan, knowledge, ... or absence of mistake or accident.” Fed.R.Evid. 404(b). The evidence of defendant’s July 1992 arrest was therefore offered for a proper purpose.
Second, the evidence was clearly relevant. Each of the offenses for which defendant was charged required the government to prove either knowledge or intent with respect to defendant’s possession of the cocaine, its distribution, or his participation in the conspiracy. Officer Garduno’s testimony — that defendant previously had been arrested for drug trafficking and found in possession of eight ounces of cocaine and $43,000 in cash— was probative of defendant’s knowledge and intent with respect to the offenses charged. See United States v. McKinnell, 888 F.2d 669, 677 (10th Cir.1989) (finding testimony of former undercover officer that he had previously purchased cocaine from the defendant “sufficiently probative of [the defendant’s] intent to support its admission”); Mora, 845 F.2d at 237 (holding that evidence of a prior uncharged drug transaction was “sufficiently related to the charge [of distributing cocaine] to establish intent, motive, and conspiracy and that the evidence did have real probative value”); United States v. Brown, 770 F.2d 912, 914 (10th Cir.1985) (holding that evidence of a defendant’s prior arrest for marijuana possession “was highly probative of [the] defendant’s scheme to possess and distribute marijuana”), rev’d on other grounds sub nom. Griffith v. Kentucky, 479 U.S. 314, 107 S.Ct. 708, 93 L.Ed.2d 649 (1987).
Third, the district court explicitly considered the evidence’s probative value and prejudicial effect under Fed.R.Evid. 403.5 The court concluded that the probative value of Garduno’s testimony was not substantially outweighed by the danger of unfair prejudice to defendant. We afford trial courts broad discretion in making rulings under Rule 403. United States v. Reddeck, 22 F.3d 1504, 1508 (10th Cir.1994). We find no reason to disturb its conclusion here.
Finally, the district court gave the jury an appropriate limiting instruction. Both after Officer Garduno’s testimony and at the conclusion of the trial, the court instructed the jury that it could consider evidence of defendant’s July 1992 arrest only to determine whether defendant had the necessary criminal intent, whether he had a motive or opportunity to commit the crime, or whether he acted according to a plan.6 This instruction appropriately constrained the jury’s consideration of the evidence. See Brown, 770 [944]*944F.2d at 914 (upholding the admission of evidence of a defendant’s prior drug arrest where the trial court instructed the jury that the evidence “was not to be considered as proof of the offense at trial, but for the limited purpose of determining motive, intent, knowledge, absence of mistake”) (internal quotation marks omitted).
In sum, the admission of Officer Garduno’s testimony satisfied all four elements of this court’s test for admissibility under Rule 404(b). Moreover, we are mindful that this court has “long recognized the admissibility of previous wrongs and crimes in the context of narcotics violations, especially when the prior activity was close in time, highly probative, and similar to the activity with which the defendant is charged.” McKinnell, 888 F.2d at 676. We therefore find that the district court did not abuse its discretion in admitting evidence of defendant’s prior drug arrest.
IV
Defendant next contends that a statement made by the prosecution during the government’s closing argument amounted to prosecutorial misconduct. Specifically, the government’s attorney stated:
I’m not here to explain court rules to you, but if [defendant’s attorney, Mr. Finzel] wanted it, he could have it. If he wanted the government to explain the timing of when his client left with the [confidential informant] during that drug deal, the timing from the exit to the driveway, when Ray Flores picks him up again visually, if he wanted to hear the timing of the Chapa-la restaurant incident, why didn’t he let Tony Lopez tell you that? I brought Tony Lopez on rebuttal, but without explaining court rules, Mr. Finzel didn’t want you to hear it. He objected when I asked the question.
An allegation of prosecutorial misconduct presents a mixed question of fact and law that we review de novo. Fero v. Kerby, 39 F.3d 1462, 1473 (10th Cir.1994), cert. denied, — U.S. —, 115 S.Ct. 2278, 132 L.Ed.2d 282 (1995).
This court applies a two-step analysis in determining whether the government’s behavior constituted prosecutorial misconduct. United States v. Lonedog, 929 F.2d 568, 572 (10th Cir.), cert. denied, 502 U.S. 854, 112 S.Ct. 164, 116 L.Ed.2d 129 (1991); United States v. Martinez-Nava, 838 F.2d 411, 416 (10th Cir.1988). First, we examine “whether the conduct was, in fact, improper.” Lone-dog, 929 F.2d at 572. If so, “we must then determine whether it warrants reversal.” Id. In this case, the district court concluded that the prosecutor’s statement was, in fact, “improper counsel argument.” It found that “the prosecutor’s comments implicitly supported] the conclusion that if Tony Lopez had been allowed to testify concerning the timing of the controlled buy he would have been a credible, truthful witness.” The court nonetheless concluded that the statement did not warrant reversal because, in the context of the entire trial, the error was harmless.
A prosecutor’s improper statement to the jury is harmless unless “there is reason to believe that it influenced the jury’s verdict.” United States v. Alexander, 849 F.2d 1293, 1296 (10th Cir.1988) (internal quotation marks omitted). In assessing whether the misconduct had such an impact, we consider the trial as a whole, including “the curative acts of the district court, the extent of the misconduct, and the role of the misconduct within the case.” Martinez-Nava, 838 F.2d at 416. To warrant reversal, the misconduct must have been “flagrant enough to influence the jury to convict on grounds other than the evidence presented.” United States v. Lowder, 5 F.3d 467, 473 (10th Cir.1993); see also United States v. Manriquez Arbizo, 833 F.2d 244, 248 (10th Cir.1987).
The prosecutor’s statement in this ease was not so flagrant.7 First, the statement was “singular and isolated,” no more than a few brief comments in the course of a four-day trial. See United States v. Peña, 930 F.2d 1486, 1491 (10th Cir.1991); Manriquez Arbizo, 833 F.2d at 248. Second, the [945]*945district court instructed the jury on more than one occasion that the lawyers’ statements were not evidence, and that the jury had to decide the case on the basis of the evidence presented. See Peña, 930 F.2d at 1491. Finally, we agree with the district court that the record contained ample evidence for the jury to have found defendant guilty of the crimes charged beyond a reasonable doubt. See id.; Manriquez Arbizo, 833 F.2d at 248. The district court was therefore correct in concluding that the impact of the prosecutor’s statement was harmless.
V
Finally, defendant raises three additional arguments: (1) that the government failed to introduce sufficient evidence to sustain his conspiracy conviction; (2) that the evidence was insufficient to sustain his section 924(c) conviction; and (3) that the evidence seized from the building should have been suppressed because the officers executing the search violated the Posse Comitatus Act. We address each of these arguments in turn.
A
First, defendant contends that the record lacks sufficient evidence to sustain his conviction for conspiring to possess cocaine with intent to distribute under 21 U.S.C. § 846. Whether the government introduced sufficient evidence to sustain a defendant’s conviction is a question of law that we review de novo. United States v. Urena, 27 F.3d 1487, 1489 (10th Cir.), cert. denied, — U.S. —, 115 S.Ct. 455, 130 L.Ed.2d 364 (1994). We will not overturn a jury’s verdict of guilt, however, “unless no rational trier of fact could have found the essential elements of the crime beyond a reasonable doubt.” Romero v. Tansy, 46 F.3d 1024, 1032 (10th Cir.1995), cert. denied, — U.S. —, 115 S.Ct. 2591, 132 L.Ed.2d 839 (1995). In our examination of the record, we view the evidence in the light most favorable to the government without “weighting] conflicting evidence or consider[ing] the credibility of witnesses.” Kelly v. Roberts, 998 F.2d 802, 808 (10th Cir.1993). Indeed, we will “accept the jury’s resolution of the evidence as long as it is within the bounds of reason.” Grubbs v. Hannigan, 982 F.2d 1483, 1487 (10th Cir.1993).
To establish a violation of 21 U.S.C. § 846, the government must “prove that the defendant knew at least the essential objectives of the conspiracy and knowingly and voluntarily became a part of it.” United States v. Johnson, 42 F.3d 1312, 1319 (10th Cir.1994), cert. denied, — U.S. —, 115 S.Ct. 1439, 131 L.Ed.2d 318 (1995). The jury may infer an agreement constituting a conspiracy “from the acts of the parties and other circumstantial evidence indicating concert of action for the accomplishment of a common purpose.” Id. It may also “presume that a defendant is a knowing participant in the conspiracy when he acts in furtherance of the objective of the conspiracy.” United States v. Brown, 995 F.2d 1493, 1502 (10th Cir.) (internal quotation marks omitted), cert. denied, — U.S. —, 114 S.Ct. 353, 126 L.Ed.2d 317 (1993). Moreover, as the Supreme Court recently held in United States v. Shabani, — U.S. —, 115 S.Ct. 382, 130 L.Ed.2d 225 (1994), section 846 does not require the prosecution “to prove that a conspirator committed an overt act in furtherance of the conspiracy.” Id. at-, 115 S.Ct. at 383.
The record in this case reveals sufficient evidence for a rational trier of fact to have concluded that defendant knew the essential objectives of the conspiracy and voluntarily became a part of it. First, the record shows that all three defendants lived on a ranch together, that all three possessed keys to the building where the cocaine and drug paraphernalia were found, and that Officer Flores had previously observed defendant and codefendant Carmelo Rojas enter the building together. Second, Officer Flores testified that, in searching the building, he seized from Rojas a marked $20 bill that the confidential informant had given defendant in the controlled buy of cocaine June 11, 1993. Finally, as discussed earlier, Officer Garduño testified that defendant had previously been arrested for drug trafficking and had been found in possession of eight ounces of cocaine and roughly $43,000 in [946]*946cash, indicating that defendant knew the objectives of the conspiracy. Viewing the record in the light most favorable to the prosecution, we conclude that there was sufficient evidence for the jury to have found beyond a reasonable doubt that defendant conspired to possess cocaine with the intent to distribute.
B
Defendant next claims that the evidence was insufficient to sustain his conviction under 18 U.S.C. § 924(c)(1) for using or carrying a firearm during and in relation to a drug trafficking offense. Section 924(c) states that “[wjhoever, during and in relation to any ... drug trafficking crime ... uses or carries a firearm, shall, in addition to the punishment provided for such ... drug trafficking crime, be sentenced to imprisonment for five years.” 18 U.S.C. § 924(c)(1).
This court has held that, for purposes of section 924(c), a defendant “uses” a firearm “during and in relation to” a criminal undertaking when the firearm “(1) is readily accessible, (2) is an integral part of the criminal undertaking, and (3) increases the likelihood that the criminal undertaking would succeed.” United States v. Hall, 20 F.3d 1084, 1088-89 (10th Cir.1994). To show that a firearm was readily accessible, the government must demonstrate that it “was available to the defendant in the vicinity where the drug trafficking offense took place.” United States v. Parrish, 925 F.2d 1293, 1297 (10th Cir.1991); see also United States v. Coslet, 987 F.2d 1493, 1495 (10th Cir.1993) (‘“Access’ to a firearm requires only that the weapon be available to the defendant in the vicinity where the drug offense occurred”).
The government can demonstrate the ready accessibility of a firearm by showing a close proximity between the firearm and the drugs. Hall, 20 F.3d at 1089. For instance, in United States v. Conner, 972 F.2d 1172 (10th Cir.1992), this court held that evidence that the drugs were “directly below the firearm” was “sufficient for a jury to find that [the defendant] intended the weapon to be readily available for use during the drug transaction.” Id. at 1174. And in United States v. Hager, 969 F.2d 883 (10th Cir.), cert. denied, — U.S. —, 113 S.Ct. 437, 121 L.Ed.2d 357 (1992), we upheld a defendant’s conviction under section 924(c) where the firearms were in close proximity to the drugs and there was substantial evidence connecting the defendant to the building where the drugs and the firearm were seized. Id. at 889.
In this case, Officer Flores testified that the officers discovered the firearm on top of the water heater right next to six ounces of cocaine. This testimony alone is sufficient evidence for the jury to have concluded that the weapon was in close proximity to the drugs and therefore “readily accessible” for purposes of section 924(e).
The two remaining elements of the section 924(c) test — that the firearm be an integral part of the criminal undertaking and that it increase the likelihood of the undertaking’s success — require “a nexus between the readily accessible gun and the offense.” United States v. Dahlman, 13 F.3d 1391, 1401 (10th Cir.1993), cert. denied, — U.S. —, 114 S.Ct. 1575, 128 L.Ed.2d 218 (1994). As an appellate court reviewing for sufficiency of evidence, “we presume a nexus between a firearm and a drug trafficking offense when an individual with ready access to a firearm is involved in such an offense.” United States v. Holland, 10 F.3d 696, 699 (10th Cir.1993), cert. denied, — U.S. —, 114 S.Ct. 739, 126 L.Ed.2d 702 (1994); see also Coslet, 987 F.2d at 1495; Parrish, 925 F.2d at 1298. “However, a defendant charged with a drug trafficking offense may overcome this presumption by presenting some evidence suggesting the firearm was present for a reason other than facilitating the drug operation.” Parrish, 925 F.2d at 1298; see also Coslet, 987 F.2d at 1495.
In this case, defendant has offered no other explanation for the presence of the firearm. We therefore conclude that there was sufficient evidence for the jury to convict defendant of using a firearm in relation to a drug trafficking offense in violation of 18 U.S.C. § 924(c)(1).
C
Finally, defendant argues that, because an Air Force sergeant took photo[947]*947graphs of the items seized at the building and videotaped the arrest scene, the officers conducting the search violated the Posse Comitatus Act, 18 U.S.C. § 1385,8 and the evidence seized during the search should therefore have been suppressed. Defendant, however, failed to raise this argument in his motion to suppress evidence before the district court. The Federal Rules of Criminal Procedure require defendants to make motions to suppress evidence prior to trial, Fed. R.Crim.P. 12(b)(3), and dictate that the failure to do so constitutes a waiver thereof, Fed.R.Crim.P. 12(f). And this court has held that Rule 12(f)’s “waiver provision applies not only to the failure to make a pretrial motion, but also to the failure to include a particular argument in the motion.” United States v. Dewitt, 946 F.2d 1497, 1502 (10th Cir.1991), cert. denied, 502 U.S. 1118 (1992).
Having failed to include his Posse Comita-tus Act argument in his motion to suppress, defendant has waived the claim. We therefore will reverse the district court only if its admission of the evidence constituted plain error. United States v. Davis, 55 F.3d 517, 520 (1995). That is, the admission of the evidence must have been erroneous, and it must have “affeet[ed] the fundamental right of ... defendant to a fair and impartial trial.” Id. We find no such error here.
VI
For the aforementioned reasons, we find no error in the judgment of the district court. The magistrate was sufficiently neutral and detached, the district court did not abuse its discretion in admitting evidence of defendant’s prior drug arrest, and the prosecutor’s statement during closing argument was not prejudicial to defendant. In addition, the record contains sufficient evidence to sustain defendant’s conspiracy and firearm convictions, and defendant has waived his Posse Comitatus Act claim. The judgment of the district court is therefore AFFIRMED.