dlls in SysWOW64 not found by application

I'm developing a C#/WPF app that talks to a USB device using some custom 32 bit dlls. It's developed as an x86 app, and installed with WIX. When I install the package on a 64-bit machine, the program files get installed to Program Files (x86) as I expect.

The dlls are installed to the SystemFolder using WIX. On 32-bit machines, this means C:\Windows\System32. On 64-bit, they end up in C:\Windows\SysWOW64. This is ok, but when I run my app, it is unable to find the dlls (it uses them via [DllImport...]).

So, what is the right way to make my app find the dlls, whether they are in System32 or SysWOW64?

Thanks
Tom

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