--- ptraj.c	2010-03-16 12:55:06.854939209 -0400
+++ ptraj.c	2010-03-16 16:15:09.786087889 -0400
@@ -5824,6 +5824,7 @@
     stopsol  = (int *) safe_malloc(sizeof(int) * state->atoms);
 
     buffer = NULL;
+    mask = NULL;
     while ( (buffer = getArgumentString(&argumentStack, NULL)) != NULL ) {
 
       if (byres) {
@@ -5914,7 +5915,7 @@
 
       }
 
-      safe_free(mask);
+      if (mask!=NULL) free(mask);
       safe_free(buffer);
     }