IF ELSE IF END gives Unclosed Function error

I am looking at PICO-8 for the first time.

This simple IF statement give me the error "UNCLOSED FUNCTION AT LINE 1".

function MYTEST() 
  local x = 1
  if x==1 then
    print("x==1")
  else if x==0 then
    print("x==0")
  end
end

I admit the function is of no use but the interpreter won't allow it to run.

Why?

As mentioned in the comments, changing the code from else if to elseif makes it work.

Alternatively, add an end before the first end:

function MYTEST() 
  local x = 1
  if x==1 then
    print("x==1")
  else if x==0 then
      print("x==0")
    end
  end
end