Hello, I would like to use Storable and declare an instance for a struct available in a C library instance Storable Parameter where sizeOf _ = #{size HklParameter} peek ptr = alloca $ \pmin -> alloca $ \pmax -> do cname <- c_hkl_parameter_name_get ptr name <- peekCString cname value <- c_hkl_parameter_value_get ptr unit c_hkl_parameter_min_max_get ptr pmin pmax unit min <- peek pmin max <- peek pmax return (Parameter name value (Range min max)) but when I try to compile this, I get this error message C.hsc:507:15: error: invalid application of ‘sizeof’ to incomplete type ‘HklParameter’ Indeed the C library do not expose this struct internal. So I would like to know how to handle this kind of C struct with Storable. thanks for your help Frédéric