tempoWholesPerMinute no longer working

[Graham King]

If I adjust the comments in the following code, \tempo works fine but
tempoWholesPerMinute has no effect.  Has anyone else seen this?

\version "2.17.95"
\score {
    \relative c' { c d e f }
    \layout {}
    \midi {
        %tempoWholesPerMinute = #(ly:make-moment 180 4)
        \tempo 4 = 180
    }
}