diff -ru orig/AmberTools/src/ptraj/ptraj.c amber12/AmberTools/src/ptraj/ptraj.c
--- orig/AmberTools/src/ptraj/ptraj.c	2013-05-02 13:16:23.000000002 +0200
+++ amber12/AmberTools/src/ptraj/ptraj.c	2013-11-18 16:11:07.140474533 +0100
@@ -1923,7 +1923,7 @@
    void
 atomMaskIsActive(int *mask, ptrajState *state, int *activep, int *firstp)
 {
-  int i, active, first;
+  int i, active, first = 0;
 
   if (mask == NULL) {
     *activep = 0;