Hi Esteban, Previously, I was doing with NB something like this: *pointer := NativeBoost allocate: 4.* *self primitiveWhatever: pointer* and: *primitiveWhatever: pointer* * <primitive: #primitiveNativeCall module: #NativeBoostPlugin error: errorCode >* * ^ self nbCall: #( int void (NBExternalAddress pointer ) )* But of course that doesn't work with latest FFI. So I tried instead: *pointer := ExternalAddress allocate: 4.* *primitiveWhatever: pointer* * <primitive: #primitiveNativeCall module: #NativeBoostPlugin error: errorCode >* * ^ self nbCall: #( int void (ExternalAddress pointer ) )* But then I get a ExternalAddress class #asExternalTypeOn: which is sent in FFICallout >> resolveType: Any idea how can I use ExternalAddress in the signature of the FFI primitive call? What am I doing wrong? Thanks in advance, -- Mariano http://marianopeck.wordpress.com