Merge a png on top of a gif with shell

I am trying to merge a png with a gif (put the png on top of the gif) and then have the result as a gif. I played around with convert, but cannot quite get it to work the way I need it. I have tried these commands so far:

convert layer1.png layer2.gif -append mergedLayers.gif
convert-im6.q16: memory allocation failed `layer2.gif' @ error/gif.c/ReadGIFImage/1303.

Anybody got an idea?