Hugo troubleshooting: execute of template failed: can't give argument to non-function

$ HUGO_ENV="production" hugo
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ERROR 2021/05/05 15:01:35 render of "page" failed: execute of template failed: template: blog/single.html:2:3: executing "main" at <.Render>: error calling Render: "foo.md:7:15": failed to execute template ["content"] v: ".../blog/content.html:7:15": execute of template failed: template: blog/content.html:7:15: executing "blog/content.html" at <(.Params.showLastmod) (ne $.Date $.Page.Lastmod)>: can't give argument to non-function .Params.showLastmod

{{ if and ((.Params.showLastmod) (ne $.Date $.Page.Lastmod)) }}

{{ if .Params.showLastmod }}
{{ if ne $.Date $.Page.Lastmod }}
...
{{ end }}
{{ end }}