How to terminate compose key sequence?

I tried adding this compose key sequence to my ~/.XCompose :

: "Λ" U039B # GREEK CAPITAL LETTER LAMDA

I then tried to use this in a few places, but the sequence would never terminate. That is, the prompt indicates that I'm not done typing the full compose key sequence, even though it's already shown: The above is from GNOME Console, which shows an underscore under the current character while typing a compose key. It seems the underlying issue is that the compose key sequence above is a *prefix* for another compose key in [X11 library root]/share/X11/locale/en_US.UTF-8/Compose:

		: "🖖"	U1F596 # RAISED HAND WITH PART BETWEEN MIDDLE AND RING FINGERS

How do I tell the application to *end* a compose key if it's the prefix of another compose key? Is this even possible, or do all compose keys have to avoid being prefixes for all others? Pressing the compose key again (Caps Lock in my case) did not help, and pressing Esc just cancels the compose key.