University Hospital Coventry is undergoing remedial work because its structures "were not as robust" as originally planned.
The hospital trust says interim safety measures are in place during the work.
Skanska, which built the hospital under a private finance initiative (PFI) scheme, declined to comment.
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David Eltringham, chief operating officer at University Hospitals Coventry and Warwickshire NHS Trust, said: "We can assure our patients, staff and visitors that we remain vigilant in ensuring fire safety standards are maintained at all times."
He said the trust "learned of some potential issues with the infrastructure" which prompted the internal investigation.
The investigation found that "in the unlikely event of a fire, the structures to prevent it spreading were not as robust as those specified in the original plan for the building", Mr Eltringham added.
The trust says it collaborated with Skanska to identify remedial work and is working with the fire service to optimise fire safety standards.
Meanwhile, steps are being taken to strengthen fire safety including additional patrols and increasing rubbish collections.
A West Midlands Fire Service spokesman said: "We are working together with University Hospital Coventry and have an action plan in place for upgrading fire standards."
Construction firm Skanska, which was paid to build the hospital, said it had nothing further to add to the statement issued by the trust.

The weather service said flooding could happen in the east after heavy rains set in on Thursday.
The amber warning has been issued for counties Antrim, Armagh, Down and Londonderry.
It is valid from 10:30 GMT on Thursday to 08:00 GMT on Friday.
Anyone affected is asked to contact the flooding incident line on 0300 2000 100.
There have been reports of flooding in County Down, near Helen's Bay and on the A1 near Newry, as well as the B72 between Castlederg, County Tyrone, and Ederney, County Fermanagh.
Trafficwatch Northern Ireland said that, due to flooding, the Foyle Road in Derry was closed between Craigavon Bridge and John Street roundabout. Motorists are advised to use the upper deck of Craigavon Bridge.
The A2 Dunluce Road is closed between Portrush and Bushmills due to a landslide. A diversion is in place via Ballybogey Road and Priestland Road.
The Ballyquin Road in Limavady is closed due to flooding. A diversion is in place via Drumrane Road and Baranailt Road.
There is flooding on the Mill Road in Limavady, however, the road remains passable with care. Broad Road in Limavady is also closed due to flooding.
It has been reported that the A2 Dundrum Road, Newcastle, in County Down is partially flooded at the entrance to Golf Links View, as is the A50 Castlewellan Road, Newcastle, at Burren Meadow.
A £380m hospital which opened 10 years ago may have been constructed without adequate fire protection, a safety review has revealed.
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There has been flooding on some roads after the Met Office issued an amber weather warning for much of Northern Ireland.