Chris Coleman wants any aggression at the England-Wales game in Euro 2016 to be confined to the pitch.
The Wales manager echoed the sentiments of Roy Hodgson and Wayne Rooney, who appealed directly to England fans to "stay out of trouble" following UEFA's threat to expel the team from the tournament.
The England manager and captain urged supporters to do everything in their power to avoid repeats of the violent scenes which marred their time in Marseille.
And Coleman made a similar appeal to Wales fans ahead of Thursday's Group B match at Stade Bollaert-Delelis in Lens.
"All we want from Welsh fans is what they always give us," said Coleman.
"That's full support, have a great time, enjoy it. Don't get caught up with anything untoward, because they're representing Wales also.
"It's not just us, it's them. They did it in a perfect way in Bordeaux against Slovakia and I'd want them to do the same again."
Coleman said he hoped the events of Marseille, where England and Russia clashed both inside and outside the stadium, would not be repeated.
However, the French authorities are on full alert with Russia and Slovakia playing in nearby Lille on Wednesday afternoon.
Lille is less than 40 kilometres from Lens and many England and Wales fans are staying in the town ahead of their game the following evening.
"We want all fans from all different countries to come and support the event and enjoy themselves," said Coleman.
"Back your team 100 per cent, but aggression should start on the pitch and end on the pitch. Off the pitch there should be no aggression.
"Unfortunately, the mindless minority do not paint the real picture. In Bordeaux our fans, the Slovakian fans and the French fans enjoyed the experience together.
"That's how it should be. All the other stuff I don't even like to talk about, I prefer to talk about what we're here to do. That's the football and it has been absolutely fantastic."
Wales began their build-up to the England game on Monday morning without goalkeeper Wayne Hennessey, who sat out training after missing the Slovakia match with a back injury.
Danny Ward made his first start as he deputised for Hennessey in Bordeaux, but Wales are keen to get the 57-times capped Crystal Palace goalkeeper fit for the England game.
"He's got a little tweak in his back, he's had it before, and sometimes these things are better than others," said Coleman.
"He's improved since Sunday. The next 24 hours will be the important stage whether we can add him to the training group from Wednesday.
"We'll see if he can come through a training session and be able to participate in the game on Thursday. We've been relaxed with him, but the next 24 hours will be absolutely crucial."
England's 1-1 draw with Russia has left them two points adrift of Wales, and Coleman's side would book their place in the last 16 by beating their neighbours for the first time since 1984.
But asked if there was more pressure on their opponents after the results of the first games, Coleman said: "Maybe from England's camp, and England itself.
"We'll go into the game as underdogs again as England will be expected to win the game. We've got to make sure there's no complacency.
"People say it's England v Wales, but what we can't do is get over-aroused by the occasion.
"Whether we're playing England or Germany, it doesn't really matter to me. We want to beat the best teams at this tournament and England are one of them."