A belt buckle assembly, especially for a seat belt system in a motor vehicle, includes a belt buckle (10) and a plug-in tongue (12) lockable in the belt buckle (10) by means of a locking mechanism. A component of the locking mechanism of the belt buckle (10) interacting with the plug-in tongue (12) inside the belt buckle (10) and/or the plug-in tongue (12) has/have design features at a locking portion (16) interacting with the locking mechanism of the belt buckle (10) inside the belt buckle (10). The design features enable the plug-in tongue (12) to be locked in the belt buckle (10) only at one of at least two possible orientations of the plug-in tongue (12) in the belt buckle (10).