Democratic Senate candidate Elizabeth Warren holds a slight lead over Sen. Scott Brown (R-Mass.) in a new Boston Globe poll released Sunday, as nearly one-in-five voters remain up for grabs with about five weeks left until Election Day.

Warren leads Brown 43 percent to 38 percent in the survey. Eighteen percent remain undecided about the two candidates, suggesting it’s still very much worth it for both to focus on the uncommitted portion of the electorate. The Globe’s May poll showed Brown up by two.

Brown has adopted a more aggressive campaign posture in recent weeks. At his first debate with Warren earlier this month, he immediately went on offense against the Democrat over her claim to Native American heritage, and later launched television ads on the subject.

Warren also has stepped up her offensive game. She recently launched her first TV ad that directly goes after Brown’s record and tied Brown to national Republicans at the debate. The same day Brown released his ad about Warren’s Native American advantage, Warren quickly released a rebuttal spot reiterating that she never sought nor received special treatment because of her heritage in her professional career.

The Globe poll is the latest survey to show positive news for Warren. After a summer in which Brown appeared to seize much of the momentum, Warren has pulled ahead slightly in recent polling, owing to increased support from Democratic voters and supporters of President Obama. But the race remains close.

The two candidates will face off Monday night in their second debate, with two remaining after that one.

The Globe survey was conducted Sept. 21-27 and carries a margin of error of +/- 4.4 percentage points.