diff --git a/proj_thresh.cc b/proj_thresh.cc
index 386035c5541fab41216ded5d305ef39b8f84cf00..fb59ee7b3af75bea406fe4e62c82088107604c41 100644
--- a/proj_thresh.cc
+++ b/proj_thresh.cc
@@ -12,7 +12,7 @@ using namespace NEWIMAGE;
 int main ( int argc, char **argv ){
   if(argc<3){
     cerr<<"usage:proj_thresh <lots of volumes> threshold"<<endl;
-    exit(0);
+    exit(1);
   }
   vector<volume<float> > tmpvec;
   //  vector<volume<float> > outvec;