query-replace-regexp on a string with '=' sign

[Pankaj Jangid]

I have a line like this,

HELLO=WORLD

now I want to downcase the part before the equal (=) sign.

I am approaching like this

M-x query-replace-regexp RET \(.+\)= RET \,(downcase \1)= RET

But this doesn't work. It works if the equal sign is replaced with
another non-special ASCII character.

Where am I wrong?