diff --git a/cpdfcommand.ml b/cpdfcommand.ml
index 145224c..5b2deff 100644
--- a/cpdfcommand.ml
+++ b/cpdfcommand.ml
@@ -608,11 +608,11 @@ let args =
    dashrange = "all";
    outline = false;
    linewidth = 1.0;
-   path_to_ghostscript = "gs";
+   path_to_ghostscript = "";
    path_to_im = "";
    path_to_p2p = "";
-   path_to_convert = "convert";
-   path_to_jbig2enc = "jbig2";
+   path_to_convert = "";
+   path_to_jbig2enc = "";
    frombox = None;
    tobox = None;
    mediabox_if_missing = false;