Compile error on Arduino MRK

[bergstar]

*: undefined reference to `InitTimersSafe()'
*: undefined reference to `SetPinFrequencySafe(signed char, unsigned long)'
collect2.exe: error: ld returned 1 exit status
Using library pwm at version 5.0 in folder: *\Documents\Arduino\libraries\pwm 

This is the same on all SAMD boards.

Same sketch for AVR compiles without issues.