A narrow majority of Maryland voters favor upholding a gay marriage law approved by lawmakers, a new poll found.

Fifty-one percent of the 813 likely voters surveyed by telephone over the past week by Gonzales Research said they favor Question 6, while 43 percent said they were opposed. Six percent said they were undecided.

Todd Eberly, political science professor at St. Mary's College, cautioned that when it comes to the issue of marriage equality, undecided voters are generally opposed.

“My gut tells me that six percent is actually opposed to it, but they didn't want to say that to someone who was asking them a question,” he told conservative radio WMAL. “I think that race is closer to 51-49.”

Large majorities of Democrats (66%) and independents (66%) support marriage equality, while a large majority of Republicans (75%) are opposed, pollsters found.

A majority of African-American voters (52%) also oppose legalizing such unions.

A July poll found less opposition (40%) to the law.

(Related: Jesse Jackson calls on Maryland voters to uphold gay marriage law.)