diff --git a/new/boostbook.jam b/new/boostbook.jam
index fa202d0bb..2ba33d16d 100644
--- a/new/boostbook.jam
+++ b/new/boostbook.jam
@@ -75,9 +75,13 @@ rule init ( docbook-xsl-dir ? : docbook-dtd-dir ? )
     {
       .docbook-dtd-dir = [ path.make $(docbook-dtd-dir) ] ;
     }
-    local boost-root = [ path.make [ modules.peek : BOOST_ROOT ] ] ;
-    .boostbook-xsl-dir = [ path.join $(boost-root) tools boostbook xsl/ ] ;
-    .boostbook-dtd-dir = [ path.join $(boost-root) tools boostbook dtd/ ] ;
+    local boost-root = [ modules.peek : BOOST_ROOT ] ;
+    if $(boost-root)
+    {
+      local boost-root-path = [ path.make $(boost-root) ] ;
+      .boostbook-xsl-dir = [ path.join $(boost-root-path) tools boostbook xsl/ ] ;
+      .boostbook-dtd-dir = [ path.join $(boost-root-path) tools boostbook dtd/ ] ;
+    }
   }
 }
 
diff --git a/v2/boostbook.jam b/v2/boostbook.jam
index fa202d0bb..2ba33d16d 100644
--- a/v2/boostbook.jam
+++ b/v2/boostbook.jam
@@ -75,9 +75,13 @@ rule init ( docbook-xsl-dir ? : docbook-dtd-dir ? )
     {
       .docbook-dtd-dir = [ path.make $(docbook-dtd-dir) ] ;
     }
-    local boost-root = [ path.make [ modules.peek : BOOST_ROOT ] ] ;
-    .boostbook-xsl-dir = [ path.join $(boost-root) tools boostbook xsl/ ] ;
-    .boostbook-dtd-dir = [ path.join $(boost-root) tools boostbook dtd/ ] ;
+    local boost-root = [ modules.peek : BOOST_ROOT ] ;
+    if $(boost-root)
+    {
+      local boost-root-path = [ path.make $(boost-root) ] ;
+      .boostbook-xsl-dir = [ path.join $(boost-root-path) tools boostbook xsl/ ] ;
+      .boostbook-dtd-dir = [ path.join $(boost-root-path) tools boostbook dtd/ ] ;
+    }
   }
 }