Johnstone has called for hopping penalties to be eliminated after VAR saved Manchester United on Saturday.
The shot-stopper pulled off a great stop when he denied Bruno Fernandes at Old Trafford.
But the penalty was allowed to be retaken after Johnstone stepped off his line.
United ace Fernandes, who hopped for the first one, repeated his technique to slot home the second time around.
And Johnstone believes that if he is punished for stepping off his line, then the penalty taker should not be allowed to 'hop, skip and jump' in his run-up.
Responding to a tweet questioning why goalies should not be allowed to move to save penalties, Johnstone added: “A striker shouldn't be able to hop, skip and jump before kicking it."