How can I vertically align a Label and TextBlock at Top so that their first lines of text line up?

<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="Auto" />
        <ColumnDefinition />
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition />
    </Grid.RowDefinitions>
    <Label Grid.Column="0" VerticalAlignment="Top">Some Label:</Label>
    <TextBlock Grid.Column="0" VerticalAlignment="Top">Some text<TextBlock>
</Grid>

The above code gives me this:

Vertically misaligned Label and TextBlock text http://img156.imageshack.us/img156/4940/labeltextblock.png

xaml label textblock
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