Ariana Grande Fan-Girled Over 'Wicked' Munchkins During Filming

Ariana Grande was in awe the first time she saw the Munchkins in the upcoming "Wicked" movie ... so much so that she stopped to take photos of them in costume.

Ricardo Ludgero Souza, who plays a Munchkin in "Wicked," tells TMZ ... Ariana went complete fan-girl before her first scene with the Munchkins, asking the actors for pics and chatting them up on set before cameras started rolling.

Ariana's reaction came as a complete surprise to the actors playing the Munchkins, Ricardo says ... she's by far the biggest celebrity on set, but geeked out over the littlest people in Oz.

Sneak peeks of Munchkinland in "Wicked" look pretty awesome ... and it sounds like Ariana was blown away too.

Ricardo spent most of his time on set filming with Ariana, and he says she totally personified her Glinda The Good Witch character ... only ever getting frustrated when she blew a take.