IE7 does not understand display: inline-block

Can someone please help me get my head around this bug? With Firefox its working fine but with Internet Explorer 7 its not. It seems not to understand the display: inline-block;.

html:

<div class="frame-header">
    <h2>...</h2>
</div>

css:

.frame-header {
    height:25px;
    display:inline-block;   
}