Rihanna has backed out of a second Diamonds world tour show, postponing a concert scheduled to take place in Baltimore on Tuesday night.  The singer's bout with laryngitis forced her to cancel a Boston show on Sunday night, and she's still under the weather.

Rihanna was supposed to take the stage at Baltimore's 1st Mariner Arena, but Live Nation says in a statement that she is "still recovering from the flu and laryngitis."  The note adds that Rihanna plans to be back on her feet for a concert at Wells Fargo Center in Philadelphia on Thursday.

Promoters are advising Boston and Baltimore fans to hang on to their tickets, while organizers work out a new concert date.