Adding a strong name to a third party dll

I've been trying to build an assembly with a strong name and had some problems as it referenced a 3rd party assembly which had been built without a strong name.

To add a strong name I disassembled and reassembled the 3rd party assmbly as follows:

ildasm /out:thirdparty.dll.il thirdparty.dll

ilasm /dll /resource=thirdparty.dll.res thirdparty.dll.il /out=thirdparty.dll /key=mykey.snk