If you’re a history buff waiting patiently for the fifth and final volume in Robert A. Caro’s series of biographies of Lyndon B. Johnson, you’re likely going to have to wait quite a bit longer.

Caro, 87, told the Associated Press that the next installment in The Years of Lyndon Johnson series won’t be coming out anytime soon.

“It is huge,” he said of the next book. “You can’t speed up the research.”

Caro series launched the series in 1982 with The Path to Power, and continued with Means of Ascent in 1990, Master of the Senate in 2002, and The Passage of Power in 2012. The books have won a host of literary awards, including the Pulitzer Prize, the National Book Award, and the National Book Critics Circle Award.

In another interview with the AP, Caro and his longtime editor, Robert Gottlieb, discussed their working relationship. A new documentary, Turn Every Page, focuses on the two; it’s scheduled to open in New York and Los Angeles on Dec. 30.

Asked whether Gottlieb has ever had words of praise for Caro, the author responded, “I can honestly say that no such remarks have been made to me.” Gottlieb replied, “He likes to believe that. I can’t imagine working with someone that long without at least saying, ‘Hey, pretty good.’”

Caro revealed that Gottlieb has pointed out the author’s predilection for a certain punctuation mark.

“He thinks I use too many semicolons,” Caro said. “That sounds small. It’s not small in our editing process.”

Gottlieb demurred, saying, “I don’t believe that’s so. He is more focused on this than I am.”

Michael Schaub, a journalist and regular contributor to NPR, lives near Austin, Texas.