diff --git a/doc/Jamfile b/doc/Jamfile
index 04fd3a5c6..9d3e0a7c5 100644
--- a/doc/Jamfile
+++ b/doc/Jamfile
@@ -50,7 +50,7 @@ boostbook spirit2
         <include>.
         <format>pdf:<xsl:param>img.src.path=$(images_location)/
         <format>pdf:<xsl:param>draft.mode="no"
-        <format>pdf:<xsl:param>boost.url.prefix=http://www.boost.org/doc/libs/release/libs/spirit/doc/html
+        <format>pdf:<xsl:param>"boost.url.prefix=http://www.boost.org/doc/libs/release/libs/spirit/doc/html"
     ;
 
 ###############################################################################