diff --git a/probtrackxOptions.h b/probtrackxOptions.h
index f3e6f6e0b4de7a198cf08d110823d82a0b166979..ca65fc0af38972e3e5a5f7d0d4e7ba0630a76e6d 100644
--- a/probtrackxOptions.h
+++ b/probtrackxOptions.h
@@ -109,7 +109,7 @@ class probtrackxOptions {
   targetfile(string("--targetmasks"), string("cmasks"),
 	    string("File containing a list of target masks - required for seeds_to_targets classification"),
 	    false, requires_argument),
-  simpleout(string("--opd"), true,
+  simpleout(string("--opd"), false,
 	    string("output path distribution"),
 	    false, no_argument), 
   pathdist(string("--pd"), false,