Setting NA in a matrix using another logical matrix

The original poster added a comment saying he'd figured out a solution, then almost immediately deleted it:

 m[ !i ] <- NA 

I had started an answer that offered a slightly different solution using the is.na<- function:

 is.na(m) <- !i

Both solutions seem to be reasonable R code that rely upon logical indexing. (The i matrix structure is not actually relied upon. A vector of the proper length and entries would also have preserved the matrix structure of m.)