Why is the icon I've placed into /usr/share/icons not displaying in the MATE Applications menu?

I have a .desktop file in /usr/share/applications with the entry: [Desktop Entry] Icon=my-app ... I have placed my-app.png into /usr/share/icons/hicolor/32x32/apps. The icon displays just fine for its entry in the MATE Application menu if I explicitly point it to the icon location: Icon=/usr/share/icons/hicolor/32x32/apps/my-app.png But it doesn't work if I use the basename: Icon=my-app Why is it failing with just the basename? This seems to be how other applications do it. I am referencing the specifications from freedesktop.org . My distro is Fedora 30. This is testing for an RPM package so I am not looking for answers that direct me to place it anywhere in my home folder.