Solution folders cause errors

PS C:\Users\Sisko\projects\dotnet-tool-slnmerge> slnmerge .
ERROR Project could not be found: C:\Users\Sisko\projects\dotnet-tool-slnmerge\src
  Referenced by: C:\Users\Sisko\projects\dotnet-tool-slnmerge\dotnet-tool-slnmerge.sln
ERROR Project could not be found: C:\Users\Sisko\projects\dotnet-tool-slnmerge\test
  Referenced by: C:\Users\Sisko\projects\dotnet-tool-slnmerge\dotnet-tool-slnmerge.sln