.NET Core - DllImport BadImageFormatException

I created project which is referencing x86 dll. But when I call the imported function it throws exception:

System.BadImageFormatException: An attempt was made to load a program with an incorrect format.

Program.cs:

[DllImport("lib.dll", CallingConvention = CallingConvention.StdCall)]
static extern int func(int a, int ab, int c, int d, int e);

static void Main(string[] args)
{
    func(0, 0, 0, 0, 0);
}

.csproj:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp2.0</TargetFramework>
    <RuntimeIdentifier>win-x86</RuntimeIdentifier>
  </PropertyGroup>
  <ItemGroup>
    <None Update="lib.dll">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
  </ItemGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.NETCore.App" Version="2.0.0-preview2-25407-01" />
  </ItemGroup>
</Project>`

It doesn't work if it targets netcoreapp2.0, but when I change the target framework to "net45" it works (I need netcoreapp because it's multiplatform)

Does anyone know where there could be a problem?