McALESTER, Okla. (AP) — Oklahoma Gov. Mary Fallin postponed at the last minute Wednesday the execution of an inmate who claims he's innocent, after prison officials said one of the three drugs they had received to carry out the lethal injection didn't match state guidelines.

A Fallin spokesman said the state Department of Corrections reached out immediately to the attorney general's office once prison officials realized they received the wrong drug for use in Richard Glossip's execution, according to Fallin spokesman Alex Weintz. Oklahoma's protocols call for the use of potassium chloride, but the state received potassium acetate instead.

Weintz said the department receives its lethal injection drugs on the day of an execution.

Attorney General Scott Pruitt's office advised Fallin and prison officials that the state's lethal injection guidelines, which had been upheld by the U.S. Supreme Court, had to be followed, said Pruitt spokesman Aaron Cooper.

"It is unclear why, and extremely frustrating to the attorney general, that the Department of Corrections did not have the correct drugs to carry out the execution," Cooper said.

Fallin reset Glossip's execution for Nov. 6, saying it would give the state enough time to determine whether potassium acetate is a suitable substitute, or to find a supply of potassium chloride.

"That's just crazy," Glossip said when told of the drug mix-up Wednesday evening. "Nobody has really told me anything," said Glossip, who said he still was in his holding cell when he learned about the postponement. He said he has been returned to his normal cell on death row and is "happy to have 37 more days."

Glossip had called a longtime friend who put the inmate on the line with reporters who had gathered for the second time in two weeks to witness his execution.

Dale Baich, an attorney for Glossip, said he was informed in a letter from the attorney general's office last month that the Department of Corrections had already obtained the potassium chloride and other drugs needed for the execution.

"Oklahoma has had months to prepare for this execution, and today's events only highlight how more transparency and public oversight in executions is sorely needed," Baich said.

Hours before Glossip was scheduled to be executed Sept. 16 for ordering the 1997 killing of Barry Van Treese, the Oklahoma Court of Criminal Appeals granted a rare two-week reprieve to review his claims of new evidence, including another inmate's assertion that he overheard Justin Sneed admit to framing Glossip.

Glossip has long claimed he was framed by Sneed, a motel handyman who admitted to fatally beating Van Treese with a baseball bat, but said he did so only after Glossip promised him $10,000. Sneed — who is serving a life sentence — was the state's key witness against Glossip in two separate trials. But the same court this week denied Glossip's request for an evidentiary hearing and emergency stay of execution, saying the new evidence simply expanded on his original appeals.

The U.S. Supreme Court also refused to block the execution Wednesday, just shortly before Fallin issued her stay.

Department of Corrections Director Robert Patton said he requested the stay after learning officials had the wrong drug "out of due diligence."

"This will allow us time to review the current drug protocol and answer any questions we might have about the drug protocol," he told reporters at the media center near Oklahoma's execution chamber before walking away without taking questions.

Patton took over as head of the corrections department in January 2014. That April, Clayton Lockett writhed and struggled against his restraints after an intravenous line was improperly placed. Lockett died 43 minutes after his lethal injection started.

Fallin has repeatedly denied Glossip's request for a stay of execution, saying in a Tuesday statement that the state "has gone to extraordinary lengths to guarantee that Richard Glossip is treated fairly and that the claims made by him and his attorneys are taken seriously."

"He has now had multiple trials, seventeen years of appeals, and three stays of his execution," Fallin said. "Over and over again, courts have rejected his arguments and the information he has presented to support them."

Another one of Glossip's lawyers, Donald Knight, said he will use the additional weeks to press the inmate's claim that he had nothing to do with Van Treese's death.

"Hopefully the extra time will bring us more witnesses who know Justin Sneed is a liar," Knight said.

Besides his innocence claim, Glossip also has been the lead plaintiff in a separate case challenging the state's three-drug execution protocol. His attorneys argue that the sedative midazolam wouldn't adequately render an inmate unconscious before the second and third drugs were administered. They said that presented a substantial risk of violating the Eighth Amendment's prohibition on cruel and unusual punishment.

However, the U.S. Supreme Court voted 5-4 in June that the sedative's use was constitutional.

Oklahoma's protocols call for the use of midazolam at the start of an execution. It is followed by vecuronium bromide, which halts an inmate's breathing, and potassium chloride, which stops the heart.

Oklahoma first used midazolam in the Lockett execution. After that, the state increased by five times the amount of midazolam it uses and executed Charles Warner in January. He complained of a burning sensation but showed no other obvious signs of physical distress.

Oklahoma has two more executions planned in upcoming weeks. Benjamin Cole is set to be executed on Oct. 7 for the 2002 killing of his 9-month-old daughter, and John Grant is scheduled to die on Oct. 28 for the 1998 stabbing death of a prison worker at the Dick Connor Correctional Center in Hominy.

A prison spokeswoman said there currently are no plans to delay the executions scheduled for Cole and Grant.