Washington (CNN) The open enrollment period for Obamacare has been extended until December 18 for those who couldn't sign up on Sunday, the original deadline, the Centers for Medicare & Medicaid Services announced Monday.

In a statement, CMS said that out of "an abundance of caution, to accommodate consumers who attempted to enroll in coverage during the final hours of Open Enrollment but who may have experienced issues" the deadline is being extended until 3 a.m. ET Wednesday to "give consumers the opportunity to come back and complete their enrollment for January 1 coverage."

The extension follows weeks of weak enrollment reports for 2020 Obamacare plans. In a statement last week, CMS said nearly 3.9 million people had signed up on the federal exchange, Healthcare.gov, between November 1 -- when the enrollment period began -- and December 7. That's down about 3.5% on an average daily basis.

The days just before the deadline, which had been December 15 in most states, are the most crucial as Americans typically wait until the last minute to sign up.

Get America Covered, an advocacy group that promotes enrollment in the Affordable Care Act and had called for an extension due to "significant outages and increased wait times on the final day of enrollment," called the announcement "a step in the right direction."

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