test equals fails

To all,
Experiencing a problem with strings (I think).
Problem: I do not get a match on the assigned variable.

<td>
      <xsl:variable name="month">OCT</xsl:variable>
                <xsl:choose>
                        <xsl:when test="$month=JAN">01</xsl:when>
                        <xsl:when test="$month=FEB">02</xsl:when>
                        <xsl:when test="$month=MAR">03</xsl:when>
                        <xsl:when test="$month=APR">04</xsl:when>
                        <xsl:when test="$month=MAY">05</xsl:when>
                        <xsl:when test="$month=JUN">06</xsl:when>
                        <xsl:when test="$month=JUL">07</xsl:when>
                        <xsl:when test="$month=AUG">08</xsl:when>
                        <xsl:when test="$month=SEP">09</xsl:when>
                        <xsl:when test="$month=OCT">10</xsl:when>
                        <xsl:when test="$month=NOV">11</xsl:when>
                        <xsl:when test="$month=DEC">12</xsl:when>
                        <xsl:otherwise>???</xsl:otherwise>
                  </xsl:choose>

My answer is always ???. I have numerous combinations of braces without any
luck.
Thank you in advance.



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