ConvertTo-JSON an array with a single item

I'm trying to create a JSON-serialized array. When that array contains only one item I get a string, not an array of strings (in JSON).

Multiple Items (works as expected):

PS C:\> @("one", "two") | ConvertTo-JSON["one","two"]

Single Item Array (not as expected):

PS C:\> @("one") | ConvertTo-JSON"one"

Am I missing something?