diff --git a/m4/dune_docu.m4 b/m4/dune_docu.m4
index 71457b746cb25e579532d5f859c49d4791ad8690..e21fe0eb9a998a681534bbe6393bf1041434dd4b 100644
--- a/m4/dune_docu.m4
+++ b/m4/dune_docu.m4
@@ -13,6 +13,7 @@ AC_DEFUN([DUNE_DOC_PROGS],[
   AC_CHECK_PROGS([PERL], [perl], [true])
   AC_REQUIRE([DUNE_INKSCAPE])
   AC_CHECK_PROGS([CONVERT], [convert], [true])
+  AM_CONDITIONAL([CONVERT], [test "x$CONVERT" != xtrue])
 ])
 
 # searches for documentation