Index: asymptote-2.47/configure.ac
===================================================================
--- asymptote-2.47.orig/configure.ac
+++ asymptote-2.47/configure.ac
@@ -169,7 +169,7 @@ if test "x$ac_cv_use_gc" != "xno" ; then
       fi
       CPPFLAGS_SAVE=$CPPFLAGS
       CPPFLAGS=$CPPFLAGS" $INCL"
-      AC_CHECK_HEADER(gc.h,
+      AC_CHECK_HEADER([gc/gc.h],
 	AC_CHECK_LIB([gc],[GC_malloc],[
 	  LIBS=$LIBS"-lgc "
 	  AC_MSG_NOTICE([enabling system $GCNAME])],[