Assembly issue with '[' [closed]

to make it short: when I am trying to assemble my code I get this
Error: invalid char '[' beginning operand 2 '[esp+4]'
and
Error: invalid char '[' beginning operand 1 '[edx]'

The most relevant code is already in the error, however I got the code from here. To reproduce the error just use this little pattern in .section .text with the command shown below:

mov edx, [esp + 4]
lidt [edx]
sti
ret

I'm using gcc -m32 -c -o idtasm.o idtasm.S to assemble.

Thank you already for you answers,
Sincerely G3bE