How do I add something to the end of "}" if a pattern is matched?

If I have something that looks like this:

hello {sdsdsdsds} pattern {askjdasjkdjasd} hello {siadsd} pattern {iuewer} 

So if pattern if matched before {*}, I need to add a ;. Output:

hello {sdsdsdsds} pattern {askjdasjkdjasd}; hello {siadsd} pattern {iuewer};

And this is just one lines, yes.

Now, I though of something like this:

's{.*}/

But I can't quite figure out how to make sed remember the contents of .*.

Then theres this,

'/pattern\ {.*}/ s/$/;/'

But this won't work since it is only one line.