  We have measured the oscillator strength of the Ni I line at 6300.34 \AA,
which is known to be blended with the forbidden [O I] $\lambda$6300 line, used
for determination of the oxygen abundance in cool stars. We give also
wavelengths of the two isotopic line components of $^{58}$Ni and $^{60}$Ni
derived from the asymmetric laboratory line profile. These two line components
of Ni I have to be considered when calculating a line profile of the 6300 \AA\
feature observed in stellar and solar spectra. We also discuss the labelling of
the energy levels involved in the Ni I line, as level mixing makes the
theoretical predictions uncertain.
