How do I make IIS compress .svg files?

I'm trying to acomplish this in web.config:

<staticContent>
  <mimeMap fileExtension=".svg" mimeType="image/svg+xml" />
</staticContent>
<httpCompression>
    <staticTypes>
        <add mimeType="image/svg+xml" enabled="true"/>
    </staticTypes>
</httpCompression>
<urlCompression doStaticCompression="true" doDynamicCompression="true"/>

But Content-Encoding: gzip never appears in response headers. Though, compression works good for other types like CSS.