The State Division of Forestry said retardant dumped on fire lines kept the Island Lake Fire north of Mile 1231 Alaska Highway from spreading significantly.
A revised estimate put the size of the fire at 1,300 acres and officials said the fire was 35 percent contained.
Operations at the customs post were not disrupted.
''We can see the smoke from here,'' said a border protection officer at the outpost 200 miles southeast of Fairbanks. ''I don't think it's crossing the (Alaska Highway).''
A lightning strike started the fire Tuesday. No structures have been threatened but the fire is near a popular gateway to Alaska.
''We just don't want that fire moving up and down that highway all summer long,'' said Tom Kurth, fire management officer for Alaska Division of Forestry. ''There's a lot of traffic moving up and down there.''
Higher humidity, cooler temperatures and cloud cover aided the 191 firefighters.
Crews by Sunday night had cut a fire break around about 25 percent of the fire, Kurth said, including the entire south side and parts of the east and west sides. The goal is to contain the blaze by cutting a line around its perimeter and fighting it from the outside in.
There are four Type One Hotshot crews and four Type 2 crews assigned to the fire. One crew is from the Lower 48.
Dry conditions are expected to continue, as the chance of rain over the fire this week stands at about 25 percent.
''I don't work on Wall Street, but it doesn't sound look like too good of a bet to me,'' said Ted Fathauer, lead forecaster for the National Weather Service in Fairbanks.
So far this spring, 101 fires have burned more than 8,000 acres. Last year, forest fires burned a record 6.7 million acres.
