Index: trunk/psModules/src/objects/pmSourceIO.c
===================================================================
--- trunk/psModules/src/objects/pmSourceIO.c	(revision 33442)
+++ trunk/psModules/src/objects/pmSourceIO.c	(revision 33443)
@@ -1069,4 +1069,9 @@
                 for (long i = sources->n -1; i >= 0; i--) {
                     pmSource *source = sources->data[i];
+                    if (source->seq < 0) {
+                        // This can happen cmf files that have been corrupted
+                        psError(PS_ERR_IO, true, "seq < 0 for source %ld in %s", i, file->origname);
+                        return false;
+                    }
                     if (source->seq > seq_max) {
                         seq_max = source->seq;