diff --git a/configure.ac b/configure.ac
index 39506be..464755d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -38,7 +38,7 @@ PKG_CHECK_MODULES([LIBXUL],[libxul])
 # FIXME To be able to use pyxpcom we currently need
 # to link to xpcom at build time. Which involves various hacks.
 LIBXUL_SDK_DIR=`$PKG_CONFIG --variable=sdkdir libxul`
-LIBXUL_DIR="`dirname $LIBXUL_SDK_DIR`/xulrunner-`$PKG_CONFIG --modversion libxul`"
+LIBXUL_DIR="`dirname $LIBXUL_SDK_DIR`/xulrunner-`basename $LIBXUL_SDK_DIR|sed -e 's/^.*-\(@<:@0-9.@:>@\+\)$/\1/'`"
 LIBXUL_LIBS="$LIBXUL_LIBS -L$LIBXUL_DIR -lpyxpcom"
 
 LIBXUL_CFLAGS=`$PKG_CONFIG --cflags --define-variable=includetype=unstable libxul`