grep only one occurrence

I am trying to grab some content, but there are multiple instances of it in the same line. I am using this command.

grep -o -m 1 -P '(?<=sk).*(?=fa)' test.txt | head -1

However, the search ends after the second/last match. Running it on Ubuntu 14.04.2

test.txt: skjahfasdkl aklsdj laks skjahfasdkl aklsdj laks
Current Output: jahfasdkl aklsdj laks skjah
Desired output: jah