Retired Lt. Gen. Michael Flynn has been an informal foreign policy adviser to Donald Trump for months, but says the presumptive Republican presidential nominee has yet to heed one major piece of advice.

“There must be more precision in the use of the language that he uses as the potential leader of the free world,” Flynn, who previously served as director of the U.S. Defense Intelligence Agency, told Al Jazeera’s “UpFront” in an interview released Thursday.