Germany goalkeeper Marc-Andre ter Stegen lamented his "unlucky" error in the side's 3-1 friendly defeat to Slovakia on Sunday.
Mario Gomez put the hosts in the lead at the WWK Arena in Augsburg via the penalty spot but Slovakia hit back just before the half-time break.
Napoli's Marek Hamsik found an equaliser in the 41st minute before Michal Duris put the visitors in front, but the costly error came for Slovakia's third goal in the 52nd minute.
A volley from Juraj Kucka bounced twice on the wet pitch in front of half-time substitute Ter Stegen, and the shot-stopper saw the ball trickle through his legs and into the net.
"It was an unlucky situation, of course," the Barcelona goalkeeper said.
"The ball bounced two times and I didn't see it anymore because of the water.
"For sure, it's my failure. No question."
Germany face Hungary on Saturday in their final warm-up game for Euro 2016, where they will come up against Ukraine, Poland and Northern Ireland in Group C.